"Going south" can make perfect sense as a form of risk management. If for instance you have 40BI for the stakes, you are playing, you are potentially risking 2,5% of your
bankroll on a single cash game hand, which is fine.
However if you are sitting with 300BB, because you won some pots, and someone else has you covered, now you are suddenly potentially risking 7,5% of your bankroll on a single hand. Which is not really good bankroll management.
However on regular tables "going south" typically means changing to another table, as most poker sites wont let you buy back in for less, than you left with. So if the table is good, you need to evaluate, which is more important.
At Zoom you can just hop in and out, and I think, there is a strong case to be made for doing it, unless you are playing for money, you truly dont care about. I still have painfull memories about some Zoom spots like running second set into top set and getting stacked for 250BB.