I think Gwindor is right at least 90% of the time with that assessment. I think there are a couple instances where the benefits of a long laning phase outweigh the team gold and innate map advantage of taking out a tower. Someone like nasus for example would rather have laning phase last 25 minutes than kill a tower in 14 just because hes destroying his opponent.
--
~Ç~ http://img.imgcake.com/AlecTrevylan006/fdshieldpngyn.png Eff_Dee
http://img.imgcake.com/nio/9fdpngys.png