You don't have to use email just to send and receive emails you can use it for many other things.
You can create email messages that you never send.
Why would you want to do that? To write yourself notes that you can reference to later on. Why do that when you can just type up a document and save it? Because if you're type up a document and save it, where did you save it to? And even if you do remember where you've saved it to, it's only on the one device. Whereas your email you can get to it from multiple devices and even from somebody else's devices, if they allow you to. You just have to login to your email account.
Such emails do not have to be part of your normal inbox, or sent mail. They can be in the Drafts folder or you can create other folders and move them from the Drafts folder to the created folder.
Another benefit of using emails to type notes, is if you use something like Gmail, you can search through all your emails for a specific word virtually instantly. Whereas if the notes were stored on your computer it would take a very long time for it to find it via a keyword search.
If you're using email to store notes via a web based emails, you don't have to back up all your notes documents because they are in the cloud and your email provider backs them up for you. To that extent, they are far less likely to be lost by computer hardware failure.
If you don't understand any of this ask me to explain it to you and show you how to do it.