A few years back, if you worked with multiple PCs, like a desktop in your office and a laptop on the road, you ran into a hitch every time you moved back and forth between them – your stuff was always in two different versions in two different places. This was a real pain. To solve it, you were either stuck shuttling files between PCs with a flash drive (or a DVD, CD or floppy before that), or emailing the latest version to yourself with a complicated name, like “Presentation for executives FROM LAPTOP V3.doc”.