Assuming you were told to use the actor merge system to manually aggregate some things.
I wouldnt necessarily go overboard with this unless the engine is having difficulty rendering.
Generally, more parts leads to more draw calls, but also allow for better optimization in terms of occlusion (things unseen won’t be rendered/won’t cost).
If you are using a kit of some sort, with 1m wall/floor/ceiling chunks, then yes. You need to reduce the amount of calls by merging actors and/or instancing things.
Its common to make different sets of merged actors from a modular kit, and subsequently re-use the merged actors as instances to create the working level.
Also, its common to just merge and re-use whole rooms, it just depends on how one needs to access things, and how collision/interaction needs to work for the game.