If you start crafting something and then log off and back on (or simply reload the page) then when you get back into the world you end up mobile while the game continues to process your crafting action.
For example, if you start crafting 40 seasoned eggs, which takes about a minute and a half, and then you reload the page then you'll have the remainder of the crafting time to run around. Actions that are normally locked out while crafting are still locked (e.g. crafting something else) but you can collect quoins and move from place to place. When the time to complete the crafting elapses, the crafting action resolves as normal, reducing your energy and giving you the stuff.