"Usefulness" is individually defined, so the proof is in smiling at your own images.

I use a green filter occasionally to lighten (green) foliage when other elements in the image are apt to merge into that tone. Sometimes, they are helpful in differentiating between green tones, as well. For portraiture, I'd consider a green filter for a man I wanted to make more dramatic/swarthy, but wouldn't use one on a woman.