If you've ever played Fortnite on PS4, you'll be blocked from playing the newly-released Nintendo Switch version.
Playing Fortnite requires you to log into an Epic Games account. If you've already connected the account to a PSN ID, you will be greeted with the following message when booting the game on Switch (via Reddit):
"This Fortnite account is associated with a platform which does not allow it to operate on Switch. Neither the Fortnite website nor Epic Customer Service are able to change this. To play Fortnite on Switch, please create a new account."
If you've logged in on PC, Xbox or mobile, this won't be a problem.
The move is due to cross-platform restrictions. Xbox and PlayStation accounts cannot play with each other, but the other platforms can.
The kicker, of course, is there's no going back once you've linked a PSN account previously. Forcing players to create new accounts is a big ask - especially as they track seasonal progression, purchases and friend lists.