Basically when you do PoE levels. 32, 34 and 35 you receive a treasure key to open what is believed to be 3 chests at the end of each level. You can only get one key per level per week.(1 key for completing level 32,34, and 35) These extra keys are basically a reset for rewards. If you bring your own keys you can loot the PoE chests again BUT you have to complete that PoE level all over again. (You can't just loot the same PoE round/attempt of chests over and over again with keys) The keys only stack to 5 in each of your characters consumables and ONLY 5 in your vault. (20 max-ish) BUT if you continue to loot chests via farming while you have 5 treasure keys on your character they will get sent to the postmaster where he'll hold 5(per character) so technically 35 is your max. Hope this helps! Edit: apparently every streamers info was wrong about receiving one key per level per week. Sorry :/