This setting controls whether or not you will receive email notifications when new songs are added to shared playlist folders that you are a member on. In order to to avoid receiving a barrage of emails, power users might want to turn off notifications while they're transferring lots of songs between catalogs and/or playlist folders.
You can manage your email notifications by following these steps:
1. Click your profile image in the top right corner and click Account Settings.
2. Scroll down to Preferences and select the toggle next to Receive email notifications to turn them on or off.