I was a big fan of UML a while ago. I'm even OMLOMG certified. I used it extensively in large enterprise projects I was involved in.
Today, I stopped UML almost completely. Sometimes, I use the sequence diagram that I find very useful to describe interactions between systems, but no other diagrams.
I now prefer working with user stories, supported by both (only) necessary documentation written by product owner (or analysts) AND his (their) dedication to the development team to give more details as needed.
UML is a tool you can use, but it's certainly not a critical factor for the success of your projects. After many years, I now think the critical factor is the development team, no matter which tools it uses.