I have, in the last year, twice been hired then found myself way under-utilized because the company wasn't really ready to do anything with me, or the thing they hired me for fell through, or whatever. A few years ago I was brought on to a mid-sized business software company as part of an acquisition, and in the short time before I ran away was used at maybe 1/8 capacity in the most anti-productivity low-wall-cubicle open-floorplan office I've ever experienced.
Organizational/planning/managerial waste of expensive developer time is real and huge. I'd be surprised if companies the size of Google didn't do similar things some of the time, and if their management's a little more clueful than average they might even make such light-weight or non-assignments official and highly visible to make them easier to account for.