Really depends on how much riding you do and the components on the bike. Back when I was younger and more fit and riding 100+ miles a week I did a lot of maintenance. Some of it was necessary like adjusting brake pads, cables that developed slack, etc. Some of it probably wasn't but gave me an excuse to tinker.

Now I'm riding less, I find I don't need to do as much except keep the chain clean and tires inflated. I still check cables, chain slack, and stuff but they tend to need less work now.