In my and perhaps most people's opinion, putting hands together is a big problem. In my case, it's THE ONLY problem.
Hands separate is fun and easy. I am again speaking from my experience, but I suspect it's most people's too.
Hands together is difficult and we better talk about it because when putting hands together:
1-You can't see both hands at the same time,
2-You can't control both hands at the same time, or it becomes exponentially difficult when hands are put together. The human mind has a hard time working that way,
3-Reading the score needs mind swithing back and forth,
4-and, to make that worse, you have to read both clefs at the same time in many pieces,
5-and, to even top that, notes are in different positions on the treble and bass clefs.
6-depending on the piece, you all can add to the list.
So with all reasons making hands together a pain, I am sure you'll want to share your secrets with us. Thanks!