The ability to sync content, whether it's photos, videos, or other files and have it available when I need it, on all of my devices, is amazing. It's fast, secure, and reliable.
I have experienced some issues storing certain files types, ie; exe files, .bat files, and some zip/rar files that contain those kinds of files. I understand the potential security issues with allowing these types of files to sync, however, it would be nice to be able to backup the installers for some of my most frequently used programs.
Also, I don't believe that you can selectively sync files to devices, it seems like it's all or nothing. Some of my devices have less storage than others, and so it would be nice to be able to retrieve only those files on demand when I need them without having to sync all of my stored data to all devices.
As a developer/tech, I frequently am creating and destroying new virtual machines and physical hardware. Being able to quickly sync all of my important data without having to manually move it all is a huge time and energy saver!