Not being native to the English language but fairly fluent in it, I'd say it's a matter of the level of style you're aiming for (and we have similar queries in Swedish). If a comma goes in before and, yet or but as phrase conjunctions, it comes out a bit more elevated - yes, could I even say it sounds kind of super-elevated, as if the writer is trying a little extra to achieve slow and imposing prose. Wasn't there a time in the 18th-19th centuries when it was more of a rule for high-style written language to give that comma before and etc?

I wouldn't use such commas within dialogue or even in inner monologue-style retelling.