Pretty much same, yeah. I guess it is better if the topic in question simply doesn't have a forum or other type of group dedicated to it. Other than that I also have no idea.
I vastly prefer Discord. It's like a "stream of consciousness" thing. Questions can just keep going and flowing while more and more people contribute. Meanwhile on a forum, that's not possible because of how messy it would be. So instead you have to make a new forum post for every thing, flooding the board with small little topics when a quick question in a Discord would do the same.
Forums feel like more work to make a topic, and more work to look through boards to find topics in case you want to answer them. Discord is just a big public discussion that keeps moving on, while important posts are pinned to be referred to easily.
But people's streams of consciousness are typically stupid garbage. A forum incentives you to actually think before you speak, which is what most people should be doing.