You could choose to backup the email data in both formats that they offer which will give you options if you ever need to extract the data.
You can also backup your Contacts or any other info that you require.
Where to save your backups is the next challenge noting that a desktop computer or laptop or hard drive has a limited life span. When the hard drive reaches its "use by date" the data is usually not recoverable. This can vary from 4 or 5 years to perhaps 10 years in some cases. So you probably need to backup important data to more than one location. This could be to a USB drive, DVDs, and another cloud service.
The final challenge is to ensure the data is secure for privacy purposes!
