There's obviously no one-size fits all model. Some things work better as metaphors, some as similes, some where the simili comes before and some after. But I think the overall guide line is the flow and the rhyme schemes. And how easily/natural stuff flows off the tongue. The standard way to use similes was to point out a double meaning with the actual thing you were saying, mostly to make it fit with a rhyme creatively. I.e. Bender is literally saying "you've been lying on those tracks". That's something he would say in real life. He would never say "you're living like a damsel in distress" or something similar cuz it makes absolutely no sense in the real world. So it doesn't really make sense to flip it. Or to say "you're living like the ugly girl in a threesome". Cuz that's not the point. The point is that he's getting fucked over. And then you find a creative way to say that thing that simultaneously rhymes.
I think as battle rap grew, and texts upon texts of rhyme schemes for years and years multiplied, sometimes you just had to flip it to make it fit with a rhyme scheme. And then that became standard, like many things in battle rap that has just become cliché, like flipping letters around or using 9 or 22 or 45 or whatever. But personally I prefer rap that stays as close to something true or natural to say as possible. Like old school rap did. But that's just a preference, ofc.
And on this surprise effect of the punchline: One thing is the natural part of it, but the other is that it's about the rhyme. "Damsel in distress" is an awesome rhyme. "Lying on those tracks" is not. @Virbius , I'm not sure I get what you mean with the arc of resolution. I think most of the time you don't get the full meaning of a bar untill the whole bar has been spat anyway. But I guess there's also a certain cadence in modern battle rap (e.g. from the whole iBattle crowd) with the: "You're like a damsel in distress!! ..." "Why's that?!" "... Cuz you've been lying on those tracks!!" I guess it's just an aesthetic that's quite removed from how rap on beats used to be. And once again, boils down to personal preference.
@Slayerr , I second that it's really cool to be able to have these discussions, and even to know more about how you guys judge battles. I also want to write and judge more bars, but sometimes life just gets in the way. But hopefully, there'll be a surge of activity around here at some point anyway..