Thermal builds? I mean, no one's going to run them because they've been nerfed into the ground, but I suspect the MS mod is there for builds that utilise stacking debuffs. There could also be a place for offsetting lower rate of fire caused by negative effects, or buffing larger hardpoints to fire more rapidly to line up with smaller ones.
No big uses for the mod, but some.
You can't run both thermal shock and multi-servos on one gun.
According to Inara, Multi-servos can be used on following: Pulse Lasers, Burst Lasers, Cannons, Multi-cannons, Plasma Accelerators, Rail Guns, Fragment Cannons.
Let's exclude burst lasers right away - just like rapid fire, multi-servos are less effective on bursts due to burst mechanics.
Multi-cannons have extremely potent Autoloader. There is simply no reason to use anything except it and Corrosive.
Cannons and PAs are high-damage-per-shot weapons with very slow ROF. No sense to increase it by 3%, you won't get a machine gun. Install Oversized, those meek 3% give a good boost when your damage is already high (and they would give even more on Overcharged). Not to mention there are more useful effects.
Any Fragment Cannon should use Screening Shell, no exceptions. If your frag lacks it, it's a bad frag.
For Railguns, installing anything except three "classic" mods with -40% thermal load is just plain stupid.
This leaves us with pulses. No useful specials for PVE, but Oversized is better anyway, since it doesn't add extra distributor draw. For PVP, there are some useful specials, so better use these (and if you don't need them, use Oversized).