Interestingly, unless you're large enough that your particular account moves the needle, the only thing this changes for you is introducing a delay to cash out

Interestingly, unless you're large enough that your particular account moves the needle, the only thing this changes for you is introducing a delay to cash out (which is in general a plus security-wise). If you have some nominal number of Bitcoins, say 100, then vaulting them still gives you an unsecured receivable against Coinbase and a row in their database. That that row is tagged "vault" vs. "demand deposit" doesn't particularly obligate them to segregate 100 BTC and cold store them. You still get aggregated with 10k other accounts and have your withdraws covered by a hot wallet. Also, in case a particular bankruptcy proceeding taking place in Tokyo hasn't demonstrated it enough, "cold storage" is attributed with vastly more security by Bitcoiners than is warranted. If implemented correctly it minimizes Bitcoins lost by one genre of attack, but have no doubt, there are many, many more ways to lose your Bitcoins. My guess is this is primarily marketing designed to convince people that keeping Bitcoins is safe and secondarily a product decision to reduce loss caused by poor user password management rather than by sophisticated attacks.