Yup you got it.
Covered under the category of scene management and has been used for years in other types of 3d applications.
In 3ds Max it’s called x-referencing where it solves the OBS problem. (One Big Scene).
The problem with working from the persistent level alone only 1 single developer can work on that scene project alone. Add Perforce to the mix and you have the check in and check out locks to deal with (more on this in a bit).
Using Level Streaming, aka x-referencing, you can have as many developers working on the project at the same time with out having to be concerned your going to mess up the persistent build.
Typical problem dev A and B are working in the persistent level. Dev A commits their “extensive” changes. Dev B commits their changes with out updating. Dev B changes will over write the changes made by Dev A.
Level Streaming solves this problem by eXternally-referencing the level,scene, and that reference is contained with in the persistent level of the master scene.
A and B no longer has to commit the persistent level as the file you are working on is referenced as being external. For that matter if an external file is updated the master is updated in real time.
To learn more just do a Youtube search for 3ds Max x-refercing. Different names but same use.
What else you can do.
1)An external scene can be loaded in and is by default the persistent level of “that” file which means you can add other levels that are part of the main level. So as you say you have a lighting level you can add it to the lvel being edit as a level stream and test for lighting on your edit using the lighting solution of the master.
2) A lighting level can be turned into a lighting scenario. If you label it as a scenario Unreal will generate light maps for that level. You can then have a level for day and one for night
3) Shader compiles are decreased big time as you only have to deal with the single edit level.
4) Since at some point the master will only contain the persistent level containing the external referenced file the same map can be used to create inherited assets necessary to run a custom game type. We have a level,load on bp, that loads in the flags and player spawn points for CTF.
5) My fav. A UE4 map is a UE4 map and the only real difference is the unique components and elements usually provided to the 3rd party mapper. Lets say you made Dust 2. You could have a version for all games using the UE4 engine.
Lot’s more tips but enough to get ya thinking?
As for Preforce. Being part of a large project, over the webs :D, the issue of locking out files became a problem with check in and out. Files tend to be locked out that did not need to be so we went with a manual process instead.