It also includes other functions that is not NSFW. Nothing that I personally care about but might be a deal breaker for bigger communities.

Discord breaks down the restrictions as follows:

• Content Filters: Discord users will need to be age-assured as adults in order to unblur sensitive content or turn off the setting.
• Age-gated Spaces: – Only users who are age-assured as adults will be able to access age-restricted channels, servers, and app commands.
• Message Request Inbox: Direct messages from people a user may not know are routed to a separate inbox by default, and access to modify this setting is limited to age-assured adult users.
• Friend Request Alerts: People will receive warning prompts for friend requests from users they may not know.
• Stage Restrictions: Only age-assured adults may speak on stage in servers.