When is it most appropriate to click that button instead of adding up to the same answer post? Is it dependent on time or difference in a view or something else?
On this site, adding a second answer is almost never going to be a good thing.
It is rarely useful on any of the SE sites, although on some of the technical ones where more than one solution can be presented for the same problem, sometimes different solutions can be presented in different answers.
Here it is far more likely that editing your existing answer for completeness and balance will be more appropriate than adding multiple answers.