For files as well as for emails, all your data have a permanent backup (synchronization is done every minute)
You are certain that under any circumstance, all your data can be recovered.
One version per day of any file is kept during 14 days. Thus, at any time, you can return to a previous version of your work, which can be very useful sometimes...
Regarding emails, you can restore individual emails. If you inadvertendly delete an email, it is still recoverable for 20 days. That leaves you plenty of time to notice that something is missing in your mailbox !