Rich_S said:A good dovetail gig is not cheap. Also, they take a while to set up. Definitely better if you're doing a batch of cabs; if you make them one-at-a-time, you'll be spending a lot of time on setup.
Finger joints are easier, and just as strong for amp cab purposes. The dovetail's only advantage is it looks nice - great if you're making finished wood cabs, but a waste of effort if you're covering them with tweed or tolex.