Some DLP are driven from the client side, and have deep integration with things like Microsoft Office, or Office 365, or (as you said) G-docs and Drive, others are designed to identify leaky buckets, exposed databases, data found in places that it shouldn't be, that kind of thing
The reason why the requirements especially matter in this discussion is that a lot of those products work via proxy to allow alleged prevention of loss, and other products work by detection. If the prevention proxy goes down or is misconfigured, that's a business impeding event and will be "pager goes off." The detection approach means no one is blocked if something goes wrong, but will naturally have a lag between "someone saves something they shouldn't" and any potential leak happening
So, it depends on the kinds of risk your business is willing to tolerate and the kinds of leaks you're trying to prevent or detect