I guess it depends on the context in which you are seeing the message.

For me, the most likely context is through blame or similar - I am looking at some code, and trying to understand its history. I see who changed it, when - and their commit message. In which case, only the intent is useful - I already likely know what the change does.

The "what it does" form is more useful if for some reason you're scanning commits trying to find the one that introduced some particular change. But that's not a use case I ever encounter.