Units with improved regeneration don't have to go back to base to repair, which allows them to be used more, allowing for better tactical options ("fight, retreat, regenerate, fight" is better than "fight, retreat to base, repair, fight").
Cloakbots are supposed to be weak in terms of brute force: for a similar army cost and reasonable composition, a cloakbot army will generally lose against other factories' armies in a direct fight to the death.
The intended strength of cloakbots is that they can have a tactical advantage over other factories (by having better information through sneaky scouts, information denial through cloaking/radar jamming, fast raiders, units that don't have to go home to be repaired). So the regeneration is part of the theme of cloakbots: fragile units, but with better tactical options as compensation.
