The problem with MTL, or low quality translation is because someone who uploads low quality translation can always do it faster than someone who tries to do it right, so there it feels like there's no point in doing the job properly if you can always get sniped by someone who does quick and dirty job.
If the manga is very clearly abandoned (explicit declaration of previous team, or like year of no updates) or never translated in the first place, even lousy MTL would be fine, at this point it's not worse than nothing, and at least it can generate interest.
Also I agree with DerekUlty that multiple translations can result in interesting discussions about accurate meaning of Japanese text, though I can understand that it can feel like a waste for scanlator when most people only discuss the first translation, and ignore your second one.