Tl;dr, SHS are useless outside of a couple very gimmicky builds.
Now what does this have to do with energy draw? Well, ED provides an opportunity to give SHS a bit of a purpose. How so? Consider the following:
For each external SHS, the mech gains a fixed amount of energy. Now how much? I'm not sure. Could be half a point, could be a point, etc. But the applications would be obvious: DHS are for sustained fire of hot weapons/mechs, and SHS allow for bigger alphas at the cost of cooling capacity/efficiency.
If you need some sort of Battletech space fairy science to explain that away, that's easy: as the SHS have less capacity, it takes less energy to pump coolant through them, thus freeing up energy. It makes about as much sense as it taking a damn mana bar to fuel the firing action of a mechanical cannon, but just roll with it, okay?!
Go ham, you crazy mechwarriors.
Edited by Aposiopesis, 18 September 2016 - 09:56 AM.