For banking gold, not for attacking.
Prior to logging off, fill all LCs with Cryos. Gold spent is protected from raids. When back online, fill with troops to actually use, getting a gold refund, since any other troop cost less than the Cryos.
Often used by those with Endless Reserves, since switch to Cryos (offline banking) to attacking troops upon return is instantanous. Without that, cost in reload time makes the strategy less appealing.