There's no reason for hollowing out solid brushes for "performance" reasons.
If the hollow volume is big enough, it'll even produce more clipnodes as Urby says, just wasting away the clipnode budget for no good reason.
If those brushes are world brushes, it's even less reason to do so as any outside and unseen faces will be stripped out by the compilers automatically anyway.
Manually NULLing faces is an optimisation step you only should do if you need to. Otherwise you're just wasting time that could have gone to actually building the map.