This affects the shade used to label the critter in the critter-tracker (that list below the compass), and if it's 30 or above, makes a note in the memorial log if you kill the critter.  Should probably have some representative values here or in GAME_BALANCE, with cross-reference.

If you're running Dynamic, tougher stuff takes longer to show up, but that's going to be depreciated as soon as hordes are operational.