WARNING
Here be Math and Numbers. Avast!
Let's begin with a few assumptions and work from there.
First, let us assume that a stick of dynamite contains 2.1 Megajoules of potential energy. When ignited this energy becomes heat, light, sound and kinetic energy. We shall call this conversion of chemical energy an "Explosion".
Second, let us assume that a pulse pistol overload is ten times more powerful then a stick of dynamite going off. The times we have seen a pulse pistol overload that immediately come to mind are in Won't Get Fooled Again where John popped a Scarran and in I Shrink Therefore I Am where the overloading pulse pistol was shrank before it went boom. We have seen a pulse rifle go boom before but I have yet to run the numbers on that.
So, a PP Overload = 21 Megajoules of energy released in an Explosion.
Third, let us assume that a PP overload is only 10% efficient in its detonation.
This means that a pulse pistol has 210 Megajoules of potential energy that can burn your happy enemies to death.
We know that PP's, depending on whether or not they're Winona, have between 500 and 600 shots. We will assume that not all PP's are Winona and go with 500 shots as standard.
Ergo, each shot from a PP = 210 MJ / 500 = 0.42 MJ per shot, or 420 Kilojoules of energy per pulse.
Let us introduce some physics.
The specific heat capacity of water is 4.186 KJ per KG at 25 C. This means that to raise the temperature of 1 KG of good ol' H2O it will take 4.186 KJ of energy.
A Pulse Shot has 420 Kilojoules of energy.
If a kilogram of water were to be hit with a pulse shot and all the chemical / pulse energy of that pulse were to be converted directly into thermal energy, then the water temperature would...
420 / 4.186 = 100.3344
The Kilogram of water would rise in temperature from a balmy 25 C to 125.3344 C and would cease to be water and in fact become steam.
Let us assume that, guesstimating the size of the average pulse shot, that the amount of flesh that can be damaged equals roughly half a kilogram.
This doubles the temperature rise, meaning that a shot to the torso or any other shot taken "Full on" will raise the immediate impact area's temperature by 200.6688 C. Assuming that the average human skin temperature has no effect on the change of temperature, that raises it from 33 C (Average human skin temp) to 233.6688 C.
The sudden temperature swing, not to mention the force of the impact, can cause the victim to go into circulatory shock. Every time we've seen someone shot once and drop, they may not necessarily have been dead, but were certainly on their way to being there.
We thus know that for species with soft permeable skin, such as Humans, Sebaceans, Luxans and so forth, Pulse weapons are perfect. Against more armored foes, such as Screeth and Scarrans, they prove less effective. In the case of the Screeth, due to what can be assumed to be a kind of Exoskeletal structure. In the case of Scarrans, it's due to the nature and composition of their skin.
Thinking along these lines, we know that Scarran skin is tough enough to resist direct knifing... to the point that the knife will break, albeit in cold conditions where metals become brittle.
Throughout the series, Scarrans are shown to be nigh impervious to Pulse fire. The Peacekeeper war seems to change the rules with regard to this. However, I believe there is a resolution.
We know from Crackers Dont Matter that PP's have power settings. We shall assume that an average shot of 420 Kilojoules per shot is the standard setting and that there are a variety of as yet undetermined power settings ranging from "Low" to "Earth Shattering Kaboom"

Lets assume that a PP overload is the theoretical maximum power that a PP can shoot all at once and overloads because it exceeds the amount that any PP can safely shoot.
There are 500 shots in a PP.
An Overload utilises 10% of the Chakkan oil to... overload.
Therefore, an Overload is equivalent to 50 shots from a PP.
We shall assume that the most powerful shot a PP is safely capable of shooting at any one time 35 x Normal Power.
Power settings can be altered on a PP to adjust for varying amounts of damage (IE, how badly you want your enemy dead, how tough they are, etc) with a cost to how efficient your ammo packs are. The more powerful the shots you shoot, the more of a hog it is on ammo.
At 35 x power, you are getting 420 x 35 = 14.7 MJ (!) per shot!
To put this into perspective, ONE Megajoule is the kinetic energy equivalent of a one tonne vehicle travelling at 160 KM/H (100 MP/H).
Getting hit by the blast of a pulse pistol, under these postulates, is the equivalent of being hit by almost 15 cars travelling at 160 KM/H. Ouch.
Or, to go back to the water example.
14700 KJ / 4.186 = 3511.71
Or, it would raise the temperature of 1 KG of water from 25 C to 3526.71 C and, of course, become superheated steam.
Of course, this hogs the ammo like no tomorrow. At this power setting you effectively have 14.28 shots before you run dry.
We can therefore assume that PK's use the "Standard" pulse setting at all times and adjust the power setting upwards when facing Scarrans in a time of war. It can be assumed that there are limitations to the power settings in times of peace in a similar vein to the efforts to limit the usage of depleted uranium rounds in the human military. In times of war of course, such limitations get thrown to the curb and thus we have weapons capable of downing Scarrans in relatively few shots at the cost of Ammo.
So, why didn't John adjust the settings in ISTIA? It's possible he did, it's also possible that Coreeshi body armour can disperse pulse fire or is designed specifically to be resistant to it. When John brought the frag cannon to bear, the Coreeshi went down fairly quickly... relative to the PP of course.
Summing Up
The PP is a deadly weapon. Each shot can raise the temperature of a 500 gram mass of flesh by 200 C, effectively cooking it and potentially sending the victim into circulatory shock. The weapons can be overloaded to provide a blast ten times more powerful then a stick of dynamite. It has a variety of power settings that can be adjusted to suit the relative toughness of an enemy, though it comes at the cost of expending ammo far less frugally. Variants can allow for greater accuracy, efficiency (and effectively more ammo) and power, and is THE sidearm that every PK and desperate human will want. Ammo is fairly plentiful throughout the uncharted territories and with regular maintenance a pulse pistol will remain a faithful death machine for as long as its user lives.
>_>
<_<
Buy yours today!
Feel free to poke holes in my assumptions or find where my extrapolations thereof fall down and fail. I welcome it.