That would be great when you want to quickly rearrange your chests around without the hassle of using another chest to empty the content first. The way I would see it is that you hold it over your head and can't do anything else until you put it down. Which mean that it can't be moved island to island unless you put bridges first.
I like making lil mock up when I do suggestion, so here you can see that the chest is "lock" in the toolbar. Tho it could be also outside of it like a 11th item that doesn't actually count in your inventory.