The game includes built-in cheat modes -- Invulnerability, unlimited ammo, no collisions. That's all we'll ever need... except that enabling the first two at any time during a mission reduces your score for that mission by 90%! Ouch.
So basically, all I'd want from a trainer is to disable that scoring penalty, or to access the cheat functions but bypass it.
Yup, that's why I want it.