I have two out of necessity. One for my Canadian iTunes account, the other for my American. I no longer use my Canadian one as I live in the us now. However, if I want to update apps purchased from my Canadian account, I have to switch. This is painful. Switching means settings like match get switched off and aren't turned back on when I move back over. It means syncing gets disabled. It means if I switch before other downloads are finished, apps are stuck in a half state of downloading but having stopped. I have to delete them and download the again. The app store icon will of course show me how many apps need updating across all my accounts. However, I can't use the update all button because I'll be asked to log in with the right account. As mentioned before logging in to another account while apps in the previous account are downloading will usually cause problems. Logging in is painful as well. After logging in with a new account, it doesn't just log you in. No. It tells you your apps is associated with a different store, despite being on the update page, and whisks you off to some other location, which then needs to load before becoming responsive again before you can go back to the update page again. There, you staart the whole thing over again.

On the other hand, Steam doesn't care and works just fine.