Camouflage helps you see before being seen, which is quite important for survival.
>CAMO: A unit is only visible from a number of tiles closer than spotter's vision range. Two values mean different effectivity at Day/Night.
>INVIS: Invisibility is something on a different level altogether. These units are only visible from a number of tiles specified, not a tile further.
>SPOT: Reduces both by its value, can differ Day/Night.
Camouflage doesn't work if you're on fire.