Raid Group
The only problem is finding the balance. It can’t be too difficult (see: Ascalonian Catacombs) or people just won’t do it. It can’t be too easy (see: Zerging in WvW) or it’s just a zergfest.
If you were to take Fractals and make it 10 man, people would be able to get to much, much higher levels so much easier because there would be more reflect uptime, more ressers, more buff transfers, more AoE, more damage, etc.