The best of 3 format is used to save time for the tournament and energy for the players. Right now, it is best of 5 for the men's finals only and best of 3 for all other matches. As we saw yesterday, though, the lack of a tiebreaker in the deciding set can make some matches like the Raonic-Tsonga match to last much longer than ordinary 3-set matches.
A good compromise would be to make it best of 5 for the semi-final, final, and bronze matches. The reason for this is that the top few players may be so close in ability (as is the case with Federer, Nadal, and Djokovic), that they deserve the fair competition offered by the best of 5 format, at least for the semi-finals. Djokovic might have had a better chance in his semi-final against Nadal in 2008, if this were the case.