Short answer: schedules help you grow/keep an audience, especially if you don't update frequently -- people won't give up on the comic if they know when they'll next hear from you. But they are not quite as important on Tapastic, where people don't have to remember to come back and check your website.
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I do wanna point out, a slower schedule is still a schedule! If your martial arts practice is pretty consistent (i.e., you know when classes are and you know how much you need to practice), you could take the time to draw, say, 5 pages while also keeping up with martial arts practice, and see how long those 5 pages took, and get a pretty good idea of what kind of schedule you WOULD be able to keep.
THAT SAID, there are a lot of creators who CAN'T promise a schedule (health issues that flare unpredictably, freelance work that comes and goes in spurts) and I've definitely seen creators who didn't hold themselves to a particular update day work out fine -- you just HAVE to give your readers a way to be alerted when you update, or they have to have a vague idea of when your updates will be ("once a week without warning," for example, if you can't promise a specific day). On Tapastic that first one is easy -- a subscription system is built in -- so it's a lot easier to get away with random updates than it would be on a standalone website! But you can also just tell people to follow you on social media for updates for the same effect.
I do think that if you can't keep a schedule, it's a bad idea to claim to keep a schedule that you can't follow through on. Updating randomly is much more forgivable to most audiences than saying "I update on Mondays" and constantly pushing your update back to Wednesday week after week.
I mean, that depends on why you're making comics. If you can only inconsistently update one page a month, for example, and your goal is to attract a large readership and eventually make a business out of it, then yes, I would tell you not to bother, because that update schedule is gonna make it very slow going.
But if you just enjoy drawing, have a story or some jokes you wanna tell, and you want to share that with people? Heck, there's no reason you have to have a schedule for that! Do it! You'll find people who love your work and are willing to wait for it. : )
Besides, by the end of it, you'll have drawn a finished comic, and whether you drew it on a schedule or not, that's really cool!
