BSP brushes - necessary?

Should i still roughen out the level geometry using BSP brushes ?
Does this provide performance improvements (collision,visibility, maybe?) ? Or is a fully static-mesh based level feasible and encouraged ?
The documentation seems to hint at brushes being ‘deprecated’ and not needed anymore.

Since BSPs have been greatly improved compared to UE3, I think it’s still worth using them to block out your levels. Moreover, just have a look at Epic’s examples. They use BSPs almost everywhere. I’m not sure about performance benefits of using them though.

No. They are not nessesary. I over year haven’t used them even once. It really depends on your workflow.
I blockout everything using meshes, either simple primitives or rough shapes of what I think I will use.

Work how it fits you best!

I couldn’t say for sure, but I’ve read a few posts from Unreal Devs mentioning that the performance is actually better with static meshes than with brushes, although that might just be for certain situations.