Quote Originally Posted by Rater202 View Post
It's explicitly stated that Goku's UI form shatters every one of his limits and barriers, his "self-limiting shells," and he demonstrably grows stronger and/or more skilled as he fights using it and powers up without consciously doing so.
Where? From what I recall, Whis says UI makes the person able to attack/defend without having to think about it, a response faster than even subconscious reflexes. IIRC, Goku getting better at it was more about him "getting the knack of it" than UI instantly making him stronger... Similar to how he and Gohan spent all the time as Super Saiyan to get better at using that form.

Goku becomes stronger with the transformation because... Well.. That's what saiyan transformations do.