Do you want your posts to be limited by discords relatively short message parameters?

Do you want your RP to be "free" level?

Do you want to personally host a discord channel and monitor the posts as they come in?

Do you want to give up the clean formatting and BBC code that the forum affords? 

Do you want the mod team to be powerless to punish something that happened outside their jurisdiction?*

If you answered "no" to any of these questions, you probably shouldn't host a discord RP. From what I've seen, most discord RPs tend to be very "impulse" post driven, which isn't my cup of tea. But if that's your sort of thing, I don't see why you shouldn't.

*[sub]You can remove people from your own server, but they will have gotten away free, as they can still hang out in the RPG discord or the forum.[/sub]