The difference between Rad1 and Rfd1 I've always wondered, what are the main tactical and strategic differences between Rad1 and Rfd1 (or Rad8 and Rfd8 as black)? I know it's a subtlety, but my guess is there are some common principles that apply often.
When you move one rook to the center, the other rook, obviously, cannot cross it. If you play Rfd1, you cannot then play Rae1. And if you play Rad1, you cannot then play Rfc1. So, part of this decision is planning ahead and thinking about which other file you are likely to want a rook on.

Relatedly, if you play a move like Rae1, you are trapping your f-rook, often making it vulnerable to an attack from the bishop. Be careful before playing a move like that.

If the opponent has a bishop on g7, it is sometimes a good idea to get the rook off of the a1 square, especially if the center is not closed. This allows you to more easily play b3 or b4 without putting your rook in danger from the bishop.