A very important rule in endgames (and for that matter in all chess) is : no principle is absolute. Sometimes you have to go against the general rule for some reason that the position creates.
This being said, the general rule in bishop endgames is :
-if the bishops are of the same color, place your pawns on the square opposite to that color no matter who is better ;
-if the bishops are opposite-colored, placing your pawns on the color of your bishop favors the defensive side. [edited for clarity]
The reason for this is that assuming equal king activity, in the first case your pawns will not be attackable but your opponent's will, and in the second if all pawns are vulnerable it increases the chances for a breakthrough, thus of a win.
All this is of course applicable only in the late endgame, when weak squares are not too big a concern generally speaking.
In the particular game you linked, starting after the knight exchange move 31, Black has a more active king but the position should be a dead draw. The a5 pawn is probably lost, but if you can trade everything on the queenside before giving Black a passed pawn, all should be fine.
For that reason, 33.bxc6 ? is not a good move, because if you lose the a pawn later, Black has a passed pawn and the c pawns are still on the board. Thus I recommend simply waiting Be2-f1-e2-etc. pushing f2-f3 if threatened, losing a5 to the bishop, but preventing the black king to access d3. I guess it should hold.
In a bishop + pawns endgame, I always thought I had to put my pawns on the opposite color of the bishop of my opponent to protect them and make it useless but in the last game I played, it was not that absolute
http://www.chess.com/echess/game?id=68811810
Because all pawns were on the same color as his bishop, it was completely locked starting from move 23. But mine was able to slip through his defense on move 35 ... Bc1.
However it's true it would have been useless if all his pawns had been on white squares and that's why I played 34 ... a6.
And after taking his a pawn, I realized my pawns were vulnerable because his bishop could was no longer locked I and started to put them on black squares.
I still think it's really important to put your pawn on the opposite color of your opponent's bishop but may be not too soon in the game and it also has to be done for all pawns or the remaining pawns are really weak.
What do you think?