I wouldn't say Crusher is a waste of space 'in-universe'. But narratively she serves no function in the TNG movies, so in those she is indeed basically irrelevant. But she wouldn't be alone there.
I'd say her best schtick was always her relationship to Picard. She arguably knew the Captain better than anybody else onboard and this gave their chemisty a bit of zest. As ship's doctor though she was merely competent. She did her job well but without the flair of, say, Bones McCoy. The little character tics they did give her, like running the onboard theater company or being a good dancer, often felt a little weak compared to the dominant traits most of the other characters possessed.