First and foremost, they engage your audience and can attract new clients. Subscribers may share their progress not only within your community, but on their own social media, giving you free promotion and a huge store of UGC. This is most likely if you encourage it.
It also fosters a strong community environment, which can actually establish relationships between you and your audience, and amongst your audience members, too. This makes your subscription that much more valuable, keeping subscribers around longer.
The video community challenges even keep people coming back to your site, getting in the habit of checking in regularly, if not daily. You want to be a regular part of your subscribers’ routine, as it reduces churn and keeps your subscriber list high.