Why not? Unless the direct solve of the first side is shorter. OLL is designed to preserve the bottom layer, so they can be longer than a direct solution. For example, take the T OLL http://www.speedsolving.com/wiki/index.php/CxLL_T_O, the shortest OLL I know is (y') F' U' F U R U R', but you can solve it with (y) R B2 D R2.