Yes, customising the WordPress Nav Menu with the Walker_Nav_Menu class is pretty powerful for customising the native WordPress menu system. Without it, you just have a simple menu! But with it, you can integrate it into anything!
I’ve recently been working on a project that requires me to use Bootstrap. Yes, I know, don’t shoot me! It was a collective decision to use it because it’s a big project and it made sense to use a framework that already considered mobile first and had well-documented ways, with code examples to do things that could get any developer up and be running quickly.
Anyway, without the Walker class there is no why I could integrate WordPress and Bootstrap together without some very hacky code but, with the class it’s awesomely powerful and easy to merge the inner workings of a Bootstrap menu together with the native WordPress menu system that utilized all the features Bootstrap has to offer in terms of drop-down menus and mobile responsive considerations!
Here’s a deeper insight into the class from Scott Fennell.