The Upgrades – Gang Abilities menu description for the 'HOMIE – C.I.D.' gang ability states that:
C.I.D. can be called into the simulation using your HUB "PHONE" menu.
The A.I. will help the saints in combat.
However, it seems that aside from having hilarious dialogue with some of the other homies and following me around, it seems that C.I.D. doesn't do anything to help in combat.
Screenshot of C.I.D. just looking at me while I'm being shot at by aliens:
I've searched and found the following posts asking the same thing but they currently have no replies:
What helpful things does CID do when called to be a follower / homie?
Best Answer
According to the CID entry on the Saints Row 4 wiki,
So CID does not help in combat, and will only follow you around and have hilarious dialogue with your other homies.