I saved my side quests as my main is a Warrior so queues and bonus XP there was never a problem, plus it is faster to go through and DPS them down later when I have alts with better gear. I do leave them alone when I outlevel them and save them for the third, fourth, etc, class. The only exception was if I saw a sidequest had a big gear upgrade for me from 2.x gear, or if it unlocked an aether current.