Facebook automatically sends a notification each time someone who is not in your friend list start following you or interact with one of your posts (like, comment, share...). If you are overwhelmed by notifications of this type, then you can turn them off.
This simple procedure explains how to disable Followers Notifications on Facebook:
Log in to your Facebook account and then go to Settings > Followers. Click on the Edit button located next to Follower Notifications and then select Nobody: