In addition to actually doing your hobbies on your Mac (ie, photography, videos, music, etc...) you can use your Mac to help support your hobbies or track things related to your hobbies.
For example, if you collect something (stamps, coins, cards, etc...) you could use your Mac to list your collection, when you bought or sold items, how much you paid or sold items for, etc....so your using your Mac to help you manage your collection.
I typically use Excel spreadsheets to do this...there are other apps as well, can even be a text document, if you prefer....
Just a thought.....