@choerrybliss
Essentially, it's considered good manners not to take over any manga project another group is working on. If you do so, and they did not ghost/disappeae or dropped the project beforehand, especially if they post quite regularly, it's sniping one project from another.
Usually it's considered bad, because bad manners plus snipers tend to post shitty, if fast scanlations. On the other hand, there are scanlation groups that hoard manga titles and can't keep up with scanlating everything regularly.
(Also, you may want to ignore the drama if original scanlators point out said snipers and people make a fuss about it, because how dare they complain about sniping...)