There is a possibility that you got signed out of your email address and have forgotten the password for that ID and not Facebook, and you want to get email notifications from Facebook. So, you make a new email ID and add that to your Facebook. You have a choice to either keep both the email IDs active on Facebook or, if you don’t want this, you can always delete the old one. The choice is up to you. You will always get a notification when you make such changes on your Facebook account. To confirm these changes, you will have to go to your email account and follow the steps as mentioned in the email for confirmation.