Most of my extra contents are just random doodle I do on a daily basic to relieve my stress and prevent myself from feeling burn-out from working nonstop on my webcomic. I do have trouble keeping focus hence why I take forever to produce stuff for each update and always wait till the last minute to finish anything up. But I do enjoy working more on extra content than the actual comic itself and always try to take a little time of the day to do it. (Like my video music for my webcomic, etc, I enjoy it, my readers enjoy it, everyone is happy)
The thing is, I pressed that webcomic is just my hobby and I'm not going professional with it. That is why I keep the page count per update to a comfortable size that I'm fine working on in my free time aside from my real job. I update weekly, each update contain 12-15 pages (make up to a large canvas of over 20,000 px in height) I work on the update day to day to day to day, and in those days when I'm feeling distracted/not wanting to work on the comic, I make extra content. Pretty much filling all my art schedule with my webcomic related stuff, which I shouldn't, but I enjoy my webcomic so what is the harm?