Use sandbox account or real account for testing game center on real device

I read in Apple documents that I must use sandbox account to test game center if i'm in development environment and real account if in live environment. I'm currently using simulator game center so I use the sandbox account. I tried using my sandbox account for real iOS device to test Game Center and it worked fine. However, when I used that account again for sandbox simulator it signed into game center but Leaderboards wouldn't work. So i'm confused. If I want to test game center working on real account, I use my real apple ID account or sandbox? Or do I have to create another account just for device Game Center testing separate from sandbox Game Center simulator testing?