Like others have mentioned, my "group" uses both in-game channel and discord. Discord we use to create team sign-up sheets for future SF/TFs, chat socially, share builds and information, listen to music and of course, coordinate for harder content or badge runs. If you are on Excel and enjoy speeding content, check out the Task Force Junkies. The channel is open to join, no requirements and TFJ has a VERY knowledgeable group of leads who know their stuff! ...in fact, many of them showed the CC a thing or two back in the day.
*THIS HAS BEEN A PAID ENDORSMENT FOR TASK FORCE JUNKIES*