Before Discord I used Skype. 
Before Skype I used Raidcall. 
Before Raidcall I used MSN Messenger. 

During those times I was still on forums and still posting for whatever reason was needed. As stated above Discord is another tool that can be used to aid in the production of a post and similar chats are out there which do the exact same thing. Chatzy, Pirate/Titanpad Chat, and even Google Docs' chat are all services that can be used for the same reason and have been used for years.

So what makes discord different? It comes down to its ease of use (compared to website chats), the attractiveness of the app itself (it has a desktop and mobile app that other chats don't have), and it also protects your identity (unlike Skype). In summary it is a quality app. 

So looking at the statement [i]"Discord draws people away from the site, therefore it is bad!"[/i], I do have to wonder... 
What is this statement referring to? Does it mean that there is less OOC chatter? If that is the case then perhaps we need to evaluate the situation from a different angle and ask whether the number of posts in IC have increased due to the chat's introduction. It makes sense if you can transfer information accords to others quicker and easier. 

Whatever the case and as I said before, I previously used Raidcall (all hail the Russian programmers) and our group of friends from when I was roleplaying back in 2013/2014 had no problems or issues with a chat killing off site activity. I do believethat this is a null value debate and it is mostly because people will simply gravitate to the form of communication that they feel comfortable with.