Why do I have to invite my QQ friends to join the group?

In order to restrict the entry of strangers.

The purpose of the invitation letter is to let the group know the source of the visitors, take the initiative to send invitations, and prevent strangers from entering the disturbing group.

QQ, short for Tencent QQ, is an instant messaging software based on the Internet. QQ has covered many mainstream platforms such as Windows, macOS, iPadOS, Android, iOS, Windows Phone and Linux. Its symbol is a little penguin wearing a red scarf. Tencent QQ supports online chat, video call, point-to-point breakpoint continuation, * * * file sharing, network hard disk, custom panel, QQ mailbox and other functions, and can connect various communication terminals.