What's the deal with the quests?

Some of the quests are to familiarize you with parts of this site like the wiki. Others are just for fun.

A lot of the quests are interesting, and you often end up acquiring knowledge that you didn't know previously

They're just for fun, it feels good to raise your level 
Although sometimes you have to do a little research if you don't know the answer, and it will let you gain more knowledge 
Also some quests are designed to familiarize you with different parts and systems of the website