Latin grammar doesn't help you with English grammar, of course. Latin vocabulary can help you with English vocabulary, but the effort of learning Latin, then transferring that knowledge to English, is much larger than the effort of just learning English.

I had some Latin in school, and yes, from time to time it comes to mind when encountering a new French or Italian word. But even if you want to learn several Romance languages, I'd guess that just learning them and recognizing/exploiting relationships is easier than also learning Latin. It does add a common denominator, but it also adds a lot of cruft.