School and work can get really stressful and sometimes it can be hard to forget about it when you get home. However, if you started a hobby, it would be easier to focus on something else and forget about your worries at least for a little while.
You get to make something
Or at least do something productive in some way that's not just work.
You can completely focus on something different
If you are like me and find your major being something you always did as a hobby, it can be hard to do the same thing you do for classes for fun. So, it's nice to find something you don't normally do like sewing or knitting or a sport.
More likely than not you get to use a different part of your brain
You get to do something that different creative, physical or intellectual than what you usually do.
You learn something useful
Unless your hobby is a sport, in which case you get to get stronger.
You gain confidence
When you get good at something, you gain more confidence in general which is always a good thing.
You can join a club or talk to people about it
Socializing is always a good thing and when you are there to do a hobby it's easier to talk to others and make friends.