Most comic artists do one comic, and far too many struggle to do that. So it's exceptional when an artist goes and does multiple comics at once. Is it a good idea? Depends on the artist.
I suppose the first question is why. Why in the world would an artist attempt to do multiple, simultaneously updating comics? Since I'm not a comic artist, I can only guess, but I think it comes down to boredom.
Imagine doing the same comic, with the same group of characters for 5, 10 or even 15 years in a row. Yeah, that gets old after a while, boring to a fault. Doing another project, anything can really apply, is a solution to this problem. New characters, new situations, new stories, anything to get out of the same-old-same-old rut can help.
Which doesn't mean the new project works. Infamous for this is the Oceans Unmoving storyline of Sluggy Freelance, which was actually pretty neat and creative on it's own, but it was PART of Sluggy Freelance, and had exactly ONE character (okay, technically two) from the main Sluggy storyline. It irritated a lot of people, and brings us to the first issue with doing another comic: Interaction with the original strip. Oceans Unmoving was presented as a storyline for the main strip, literally part of it, but in reality had only a little to do with Sluggy itself.
Such a violent switch between these different projects causes fans of the normal strip to outright rebel and Oceans Unmoving was canned at the first available opportunity. Other comics do better with the split personality thing. Krakow, in it's first incarnation, split the strip into two, with the funny comic (Krakow 1.0) running MWF and the action comic (Krakow 2.0) running TTh. Eventually, though, it was split up and even now there are at least 4 comics (three done) that can be considered Krakow and another "side project" in the works that will replace Charliehorse for a time.
Krazy Krow isn't the only one that likes running multiple comics. 8-Bit Theater is actually one of four comics featured on Nuklear Power, all four of which involve Brian Clevinger. Involve, but he doesn't work solely on any except 8-Bit itself. The rest involve other people and artists, just as Marilith and the new superhero comic will be written by Krazy Krow, but not actually drawn by him. This seems to be a nice trend, actually. Sorcery 101 features three other comics in the same universe, but written and drawn by different people than the main comic. I'm sure there are other examples, but these seem to stand out to me.
On the other extreme is Adrian Ramos and his trio of projects: Count Your Sheep, No Room for Magic and The Wisdom of Moo. Now I haven't read Moo yet, so I won't comment on the quality, but CYS is much, MUCH better than NRfM, and it's updated far more frequently. But does that mean he shouldn't do it? Well no, as I said, being able to get away from the main project (CYS here) probably helps keep him active and interested. The problem is that Magic and Moo are both advertised through CYS in place of actual CYS strips. Look, I know he wants us to read the other comics, but updating CYS by asking us to read the other comics instead is a form of cruel punishment.
Of course, cruel punishment can be exacted upon the comic as well. Exploitation Now actually a good example of a new project that actually replaces the current one, but in such a way that it doesn't become obvious for a while. The fun, relatively light comic that starts the strip fades away into the angst filled action comic that ends the strip. The main characters in the beginning all be vanish by the time the comic ends (and even protest their lack of inclusion at one point). At least Poe admitted to this fact, and shut it down in favor of Errant Story.
So is it wrong to multi-comic? No, it's not, but decide where your loyalty lies before you embark on a project. For all the complaining I did about Ramos, he does focus on Count Your Sheep above his other two comics. Once you decide that, don't force the comic onto your current audience either by disguising it as part of the main comic or through very forceful ads. Explain carefully about the new project and invite them to join you on this new adventure. Be prepared to abandon it as well, after all, it's just a side project, something to get the creative juices flowing again. And as always, have fun with it.
By the way, anyone get the joke of the title? Bah, I bet you kids have no clue what it's referencing. Ah well, I'm off. See you next time kiddies.