Why need a worker for a instant building or buy?

[succubon]

I have been thinking about it and for game, money and everything it dosen't have any sense to have a worker available to buy, build or anything that will be instant.
i mean whats the point!?
I think this can be a good chance for players and for the game itself...

[paulting]

We should be able to get workers off duty or even make walls not even require a builder