A useful tool that Ive used in the past with Hammer Editor was the cordon tool. It acted as a volume which everything outside of it isnt rendered, and is not processed in the compiling of the map. This allowed for only very specific areas having light built, rendered, and allowed the user to hide areas of the level that are not needed at the time. This tool helped with performance, as well as allowing you to not waste tons of time on building an entire levels lighting, just to see how a specific section will look.
There is a good piece of documentation on the Valve Developer wiki https://developer.valvesoftware.com/wiki/Hammer_Cordon_Usage