How much of UE4/5 gets used in the final game?

Stupid Q.

I’ve taken the habit to develop parts/modules of my project in distinct project in and of themselves. The intent would be to migrate from each of those projects into the finished product. I might be playing around with different things until I get what I want so in an effort to make sure all the old-stuff is never carried forward, I’ve been of the mind to have a single project I migrate all my finished-parts into.

My thinking is that when I go through the migration process, since I can cherry-pick which items go over, I’d end up with less bloat owing to ‘scratch work’ and any associated resources…

I get this might help reduce bloat insofar as resources like textures, meshes, etc.

This make any sense? Anything this process might miss or is this kind of a non-starter?