I didnt know what was that till now. Is better have empty spots??
I think there is a middle ground between keeping your minor league levels completely full and having some empty spots that are filled with ghost players. I'm sure everyone has their own opinion. Some might say it helps to have fewer in their minors to allow the real players to develop but some might like having a full level of real players to get a good feel of who is ready for the next level. To answer your question, I don't really know. For me, I like to try to have an almost full level but it's not the end of the world if not.