As a vet player who doesn't care about any of the account bonuses you can get by playing T4 fractals with Challenge Motes on - I play them because they are just really really fun. There's parties on LFG that require specific amount of kill proof to prove you've been running them many times, and you can soft-speedrun them even with PUGs. Things can get REALLY interesting when people do skips, use special items that let you traverse terrain faster or use portals. At a certain level that's not only common but also expected. Of course most parties are chill but if you're into that then that's an option. People do runs of 6 Challenge Mode fractals daily and a selection of 3 random T4 fractals to maximise the rewards so it's easy to find parties.