Once you have 25 followers at ilevel 645, the warmill/drarwen bunker are completely useless. Till then, they are invaluable.
At this point, you should be overflowing in garrison resources and not have enough places to dump them - which makes keeping your warmill constantly working very, very easy.
There are SO few sources of getting follower gear already that turning away such an amazing resource is, well, moronic.
Well, unless you really don't care about mythic raid gear, in which case, err, go something else, like NAO.