The Employee gone "rogue"
You trust your employees with your your data and 99% of the time your trust is well placed.
Sometimes however, employees just go rogue! After they have left the company you discover they have deleted a chunk of your data.
What do you do - call Microsoft? They will again tell you that there is no guarantee they can recover all (or any) of the files and if they can it may take some time (hours/days/weeks)
With a cloud backup solution you can recover any data that has been maliciously deleted.