By common I mean actors that don’t have a visual representation as such. These are managers, spawners, etc.
If actors are visually visible on the level, or they are in different places (or something depends on their position) - then you obviously need to place them on different levels.
But remember - these are completely different objects that have different paths (different references).
Objects may have the same CLASS, but the INSTANCES you create by dragging a blueprint onto a level are not related to each other in any way (unless you do it yourself in the code of these classes).