Instead of standard notification on each new message, BP Better Messages plugin will group messages by thread and send it within next 15 minutes with cron job.
- User will not receive notifications, if they are disabled in user settings.
- User will not receive already read messages.
- User will not receive notifications, if he was online last 10 minutes or he has tab with opened site.
You can revert to standard BuddyPress notifications in plugin settings.