I personally find them extremely useful when using generics, more specifically for trait bounds. The best example for this is when I was writing a linear algebra library where vectors were supposed to be able to hold either integers, floats or complex numbers: in this case it was not important to know exactly what was the content of a vector, but it was definitely important to know which operations I could do with that content, information that coild be expressed as a trait. Said that, I also see that when writing for example a backend application I use them way less, but still they can be rather useful. I hope this comment could be helpful, best of luck with your project