Other than during a few strings by a few characters that have holes where you can parry, following some things when I'm expecting a punish, and when I have a really good read on the opponent, I haven't found a whole lot of use for it. I like it when fighting Doomsday because it can be used to counter d1's when you know they are coming and it works against his Venom charge, which is pretty easy to do. Also against Superman when I'm having trouble getting him off from corner pressure and don't wanna waste a bar, but it's risky and requires a good read. There are certain times where you are at a good amount of disadvantage where it can be good to use (following a blocked crowbar, which is -4, for instance).
The problem is the risk reward factor; your risking getting full combo punished in most cases over 11% damage and a useless buff; you only gain 11 frames of advantage knocking someone down with a successful parry as well, which isn't enough to do anything useful with in pretty much any matchup except maybe throw teeth and see what they do on wakeup. In most cases, that juice is not worth the squeeze, and it's better to back dash, jump, or block depending on the situation, because you are potentially opening the opponent up to a better punish while incurring the same risk yourself.
The only thing that thing about Joker's parry that is kinda handy is the fact that you can option select it (hold back and mash parry) when you are executing it in a tight window. If it doesn't activate, then you are still just blocking so you're fine, and if it does, parry. This is only useful, though, because they never made it usable as a wakeup/reversal like they should have.... sooooo... yeah.
Anyways, that's how I see parry right now. Take it or leave it.
