During the limit, Sora can move around freely, albeit at a slower pace, and he is not able to be harmed. Also, the targeting reticule can be aimed using the right analogue stick.
While seemingly very weak by itself, FPS Mode's true strength and purpose lies in Sora's ability to follow-up on the limit's attacks once finished, making it an effective tool for making targets, particularly bosses, vulnerable. This is congruent to Chicken Little's purpose as a Summon used to create openings.
Learning FPS Mode
Kingdom Hearts II