Disadvantages in my mind are:

*. Someone else controls access to your files
2. You have to trust someone else to protect your files.
*. You have to have faith that the someone else will be around in the future anytime you might want access to your files (i.e. doesn't go out of business, or 'pivot').

Granted, for a lot of non-********* users, that someone else can probably do #2 better. But companies go out of business all the time. Even Google changes policies. So #* could be an issue. If you're using the service consistently you'd probably get notice of a shutdown and have time to get your files. But what if you didn't?

So has anyone ever lost files due to a service provider shutting down? Yes. Getting hacked? Yes.

Has anyone lost files on their personal computer due to no backups? Yes. Getting hacked? Yes.

There are risks either way. I just feel more comfortable protecting my own data. Maybe some day huge breaches will be a thing of the past. Until then, I prefer to control access to and the security of my own data.