People can do what they want, obviously, but my preference when it comes to dialogue is to opt for shorter posts going back and forth. That doesn't mean one line of dialogue counts as a post, this isn't free after all, so you'll have to make some effort to show how your character is reacting, what they're thinking of what someone is saying, etc.
Oftentimes collaboration posts can cause problems if someone disappears mid-post and the other person is left with their (respective genitalia) left hanging in the wind. If you go back and forth it mitigates the risk of that. You have some freedom to get out of it if need be.
But if collaboration posts work best for you and you think you can deliver them in a timely fashion, do that. "Whatever works," basically.