why is one Rook move better than the other

hi all, can someone tell me why Rfd8 is better than Rad8  ?   I really struggle with understanding which Rook to move to the center files.

Black to move, so from black's perspective.

Thanks!

In general you want rooks on files where there isn't a friendly pawn blocking it.

In fact all your pieces are like this... they'd rather look at enemy pawns than look at friendly pawns which block them.

So the rooks belong on the d and c files. If you play Rad8 then the f rook can't get to c8.

Of course in some openings you'd play a move like Rfe8 here (behind your e pawn). Sometimes that's to help the e pawn advance, and it's also just good housekeeping... 

(a rook on f8 usually helps the opponent checkmate you because rooks are very awkward defenders. Much better to leave f8 open or to put a knight or bishop there when defending).

These situations are really difficult, which rook to move? In this case my thoughts would be that freeing the f8 square is useful as you may later have the option Kf8 or Bf8. You may also play the Ra8 to c8 putting it on the same file as the opponents queen. 

@sir-Foxy and @stranemover, thank you, your thoughts make a lot of sense!...wow, something actually clicked for me!

This is highly dependant on the position. See the following topic https://www.chess.com/forum/view/game-analysis/counter-intuitive-move-2-49498953 where moving Rhb8 is better than Rab8, but both make up the two best suggested computer moves.

thanks for sharing...not in million years would I have seen or played Rhb8 for exact reasons you mentioned.

I just mean that should be your first consideration... not being blocked by friendly pawns. Like I said, the same goes for all pieces. But there are many other things to consider in a position... I mean, if you take the advice too far, you'll never defend anything heh.

The most common exception would be something like this.

Where it seems natural for a rook to be on the c file, but in some cases the fact that black's rook is on the a file and white's isn't only works to black's benefit as the a5 break is very good, often backed up by a bishop and/or queen on that diagonal as shown.

Something a lot of lower rated players don't consider is that minor pieces are almost as bad as pawn when it comes to clogging files 

So for example here I'd definitely consider rooks to c1 and d1 and at some point playing c4 (depending on how black is set up of course). Not the e file because the bishops block it.

So going back to your example

I probably wouldn't be thinking of putting either rook on e8 for the same reason... the e6 bishop is nice, white's e4 pawn isn't particularly weak, and the e6 bishop blocks the file.

attacks are on the queensides, and some pawn pushes may need support on a-b files. plus there is a Bh7+ with queen support, you may need Kf8 escape later.