There are side quests that may look like they're not important ... only to find out later that they were key to getting later spells, school pets, or opening up a dungeon you may want to do later on. (Grizzleheim and Wysteria are two examples of this. Grizzlehiem looks optional but it leads to all future school pets and most utility spells beyond level 35, Wysteria leads to Tower of the Helephant, a dungeon many people like to do for the ring and athame it drops.)
Some side quests lead to training points for off-school spells, or to your own school's utility spells.
As previous poster said, if you deleted a side quest and then later find out you should have done it, you'll be confused about where to go and pick it up.
When it comes to side quests, you already have a couple of options:
1) When the quest is first offered, if you want to take a chance that it won't matter later on, go ahead and decline the quest. Hit decline instead of accept and you can walk away without the task in your quest log.
2) Take the quest and just do it ... later. That way, you won't have to worry whether it actually did matter or not. Once you complete it, the quest either leads to something else or it's gone forever from your quest log.
Never gonna happen as then KI would get flooded with questions asking "where do I get X quest from again?". If you want rid of a quest then just do it and get it over with.
How do you know it's never going to happen and what will happen if they do unless you work for them? Ki never said never. They're known to chance their mind and have a few times in the past as Technology grow. Yes they did say they will not add quest removal option in but that was said in 2010 and again in 2014 before Quest Helper was improved that same year. Now KI made it so we can tell the difference between storyline from side quests. If KI can do that, I'm sure maybe they can put locks on storyline and spell quest so we can't accidentally delete the wrong quest that would eliminate the flooding problem
I have several side quests that been sitting in my book for 3 years and I have no intention to do them. At first I thought the quests were cool to do until I fond out the bosses cheat or how they cheat beyond my taste making it a turn off. I rather not do them and delete the quests.