"Online backup services"
You can access your files online through any web browser.
Many have a mobile app so you can easily access your files on mobile devices.
Many have software to sync files to your desktop and to the services.
Very easy to use.
Never loose your files from broken or damaged hardware.
Just for normal files like pics, videos, music, PDF files... It's the best thing ever!
If you are backing up "sensitive files" (business account numbers, bank info, etc.)
You defiantly want to double check on the security level of the service (encryption)(128bit, 256bit, etc)
If you delete your files from the service many keep a backup of your files. So your files are really always in there service after you upload them. (mainly this is for in-case you didn't mean to delete something, you can restore it very easily.)
If your internet service went down you may not be able to access your files if you do not have a copy of them on your hard drive. (when does this happy though?) lol
--I Really Like Online Backup Storage Services
For me it depends what kind of files I am saving on online backup services.
If its just fun stuff like I mentioned above (music pics videos info docs) nothing sensitive. Using a service is great!!
If you have sensitive information like Bank info etc. make sure you look into the service thoroughly on how they secure your information.
Thanks hope this helps :)