Turning of lights that don't contribute to the currently rendered image will not help performance (at least not as much as you might expect), as at least all lights that cannot contribute (due to beeing in the wrong visleaf for example) will get discarded anyway.
Well I've tested this with the bucket visportaling I do and some stuff outside the bucket (that can't be seen directly) still gets rendered but only at maybe %50 of the shadow casters for some reason. So directly overhead of the bucket a single region would actually help but again it's a case by case basis. The method still needs to be weighed out with constant checking of performance stats and where different bits still render out of direct line of sight. I think the region light controlling will help to a degree but I don't think it has to be overthought either. It seems to have the best application where you want climbable rooftops and unhindered outdoor visibility. When the mission comes around to release, I'll be sure to document some of these performance steps if they end up in the mix.
Apologies for semi-derailing the thread topic, I didn't mean to get so far off on a tangent.