Parties, slots and the build that belongs in each one. Build the comp once and attach it to every event you run, instead of rebuilding a spreadsheet each week.
Drag parties into shape, set how many slots each one carries, and see the full fifty-man picture on a single screen instead of in a spreadsheet.
A role is a slot plus the build that belongs in it. Players signing up see exactly which set they'd be bringing, so nobody turns up in the wrong gear.
Comps are saved to your guild and attach to any event. Change the comp and every future event using it picks the change up.
No seat count, no trial clock, no paywalled feature. Set the guild up and run your next mass on it.