I love Discord. It's done absolute wonders for being a tool for keeping a group of players active and invested and genuine friendships to form; I think that it's kind of been so successful in my roleplay it feels weird being in another roleplay without one, and for discords to not be very active if they do have one.

I think a lot of the criticism people have for Discord stems from problems that already exist and GMs not enforcing rules and good behaviour, or creating subchannels for different purposes; on my discord I have a general chat (for just OOC hangout), a roundtable discussion (to talk about characters and posts, events that came up, etc), a collab discussion (for players to talk about planning a collab or working out details in it while writing it), and a few others that I wouldn't consider essential but are there because players requested them, like a meme channel and a nsfw channel and a music channel for sharing songs and playlists. 

I basically have a very simple rule I hold myself to; announcements get posted OOC as well as Discord, and if there's any toxic or malicious behaviour, I pretty much have a zero-tolerance policy. If someone's got a history of shit talking other people, arguing with others, and generally just being a real asshole, they're gone. Bye bye. Go find another RP to trash because it's rare to find an RP community that's genuinely mutually supportive and interested in each other as people and players alike; my RP group has frequent discussions about each other's characters, like their history and relationships, prospective interactions with other characters, their goals, etc. We talk about the posts that go up and stuff we like about them, and off topic, I like having a place where players can feel comfortable talking about anything without being judged for it. 

One thing I've seen kill so many fucking Discords and RPs and drive players away is if toxic people are tolerated; there's places on the internet to argue politics all day (let's face it, the only people who want to talk about politics all day are the ones who are so set in their ways are the ones who will never, ever challenge their views or listen respectfully to counterpoints), and I don't see how tolerating racist, homophobic, or sexist bullshit is even a thing. I can't count the number of times I've had people come to me in private and talk about being uncomfortable or feeling unwelcome by someone because of really toxic behaviour, and those people are way better roleplayers than the toxic people almost all of the time. 

Onto good stuff, I actually find discords promote a more organic discussion for RPs, and it only works if players actually try to participate, and it's that reason I kind of think that discords are best saved until [i]after[/i] the game's been established and you have core players, but I know that's unrealistic. The best thing a GM can do is to set posting deadlines and enforce it; you cannot wait for everyone, and from personal experience if you hold up a game for one or two players, you're going to lose momentum and interest fast and then your RP is at a real risk of dying. That's where Discord is handy; you can set out alerts to everyone, say "hey you have until this date to post before I move the game along" and actually have a discussion with players if they're stuck or need a hand. It's about helping everyone out, not punishing them; even if they don't make the deadline, that's perfectly fine! We all have periods where we're in a slump. 

Discord's made the RPing experience way more personal and enjoyable for me, and it's helped realize a potential I never really had with Skype or anything else. Like any tool, it can be misused and abused, and not every single RP needs to have a Discord, but for people who genuinely want to talk real time and plan stuff out organically with multiple people, it's a godsend. The GM still has to do heavy lifting to keep the game active and moving along, and you need to enforce some basic etiquette rules (keeping shit posting out of general chat and eliminating toxicity are huge ones), but not having it these days is kind of like doing math without a calculator; it takes way longer and not nearly as easy.