Is cleaning out the main sewer line a regular scheduled maintenance item?
It depends, if the sewer is well designed, well built and does not have any issues, and you don't put a lot of fat down it will be ok for a very long time with no maintenance.    

However if it "has issues" then you may wish to have it snaked before it gets blocks and becomes an expensive after hours service call.

The problem is you wont know until it gets blocked next time if you should have done the maintenance….