- That it will only work with one Google account (with three active ones, that's not very helpful).
- That when you open a file in finder/explorer it opens up a browser, which seems a rather pointless user of a desktop application.
Insync solves both of these issues, allowing multiple accounts and also doing a fantastic conversion on the fly, opening documents in your office application of choice. Formatting can sometimes be a little strange in the opened documents and I've no idea what would happen if you tried to collaborate on a document at once.
Insync also has mobile apps available, but as for some reason (android at least) they have support for multiple drive accounts, it's rendered somewhat pointless.