Imagine the scenario.
Tomorrow Facebook shuts down. Just switches off. Gone. You do not own your data, Facebook does, they have the right to just switch off and you can do absolutely nothing about it. Your videos, posts, members details, everything is gone. What do you do now? Well, that is why you get email addresses! Get the contact details of every single member and store it on a database. It is one of the fundamentals of Facebook marketing.
Important to remember though.
There are laws against unsolicited emails. If you are adding someone to your email database, you do need to put a disclaimer and an unsubscribe button. You can not just start bombarding people with emails, make sure it is relevant and make sure the content has value.
It is also better to ask people to email you if they would like to unsubscribe instead of using the unsubscribe button. Every time someone unsubscribes from your automated mails it is a black cross against you. If too many people unsubscribe your automated mail company will classify you as a spammer.
Also remember, you can backup your data on Facebook.
This should be done every few months. So if anything does happen all your pictures and videos are safe on your hard drive. You can also upload your videos to YouTube. They can be set as unlisted or private so only you can see them.