I don't think that every RP needs a discord. It is very case by case. The larger group you have the easier I find Discord is to manage information and allow people to plot. The bug advantage I have is that when I come onto the Guild now and get a notification 90% of the time it is an IC thing for me to to read, so I keep closer tabs on my RPs.

Smaller groups I tend to find OOC is best. Or if there is a RP style where you want people to not plot too much.