Well, at some point in my life i was, but that time was a verrry long time ago, i was already developping my ideas a lot, i have several comic books in my head and written down...
As you maybe imagine my drawing style takes me hours to achieve single panels, i may be able to lighten the stuff i'm doing to advance faster in the story tho and free some time for illustrations on the side.
But one might be aware that the extra stuff might not be up to par with the quality of the main story i'm working on, mainly less hatches, less shadowing etc, if i had to draw panels for a second comics while i'm doing my stuff too.
That's the reality of it for me at least.
It really depends if someone just needs illustrations, or a full blown story / comic panels on the side. (illustrations would be more worked / fine artwork but panels might be on the light side of things )
I'll add that if the writer can provide quick storyboard work with it's writting it might even be faster. (even with some kind of stick figures representing close ups, situations, etc )