What's stopping teams in chess olympiads from mixing up their board order to gain an advantage? All I could find was the rules (http://www.fide.com/FIDE/handbook/chess_olympiad_regulations.pdf) that said that the board order couldn't be switched in between rounds.
However, even without changing board order, being able to arrange the boards independently of playing strength can be used to gain an advantage. For example, suppose we had players A,B,C,D,D', where player A is stronger than player B, player B is stronger than player C, player C is stronger than player D, and player D is the same strength as player D'.
Instead of ordering the players by strength, we could put player D' at first board, and then place the remaining players by strength (so player A is second and so on).
In each round, we only play four players. If we have the first board sit out, we could get the usual board order by playing strength. However, we could also have the fifth board sit out, in which case we have shifted our top three boards down by one, which could be useful against a stronger opponent (especially one that is top heavy).