Just asking myself the exact same question and found this old thread. I have a project on Desktop and want to run on Mobile. Running into severe performance issues, caused by Occlusion. Playing with software occlusion and preccomputed visibility - helps a lot, now getting same bad performance, now being limited by GPU somehow.
The point is, that there are many changes in a level, and I do not see how to handle quite some stuff within a single project, as you say @Playasene94. On the other hand, there are scalability settings and device profiles to handle for example max texture sizes, there are material quality switches - all things, which seem to be exactly designed to handle multiple platforms in a single project.
The main question now coming into my mind:
How do you handle the blueprint/C++ code, if projects are completely separated?
Doesn’t this end up in a whole mess doing all work at least twice? Or endlessly migrating changes from one project to the other, which is error prone?