Idea is to be able to disable one of the order listed and still be able to use the "Next: Craft" button.
For instance when queuing patron work orders, there can be an order that has no interest for you in the midst of the pack.
Allowing 0 as a valid input in the Queued number would allow to just skip this entry when using the "Next: Claim/Craft/Submit" button.

Missed the middle click option to remove from Queue I guess it's not needed then :)
Maybe could use 0 as "infinite" eventually :D