A strongbox deed can be consumed twice, and each deed reduces the weight of gold by 25%. Essentially, this means you can spend longer actually hunting and less time commuting in and out of dungeons to drop gold.
One of our members, Vereth, proposed that we start encouraging new players to get their strongbox deeds before they get their mastery chain, and we’ve seen that the extra dungeon time makes an incredible difference. Prior to that, we thought of strongboxes as a late-game customization. Start saving for at least one strongbox as soon as you can.