I know I'm going to get accused of trolling, but I am going to ask anyway, in hopes that someone will give a serious answer.
Why do so many hobbyists use dovetail jigs? My experience is very limited -- early in my participation in the woodworking hobby, and with crappy equipment (Craftsman 1/4" router and Craftsman dovetail jig) so maybe that is tainting my view. But I find cutting dovetails by hand to be rewarding. And while my results are well shy of the "gee-whiz" handcut DT's you see at a woodworking show, I can pull open a file drawer in my desk and from two feet away not see the flaws in the DTs. Looking at them, I remember fondly the satisfaction of doing my first 1/2-blind dovetails. I don't think I would get that from looking at precisely milled and "sterile" dovetails.
I understand the appeal of a jig for production work, where time is money. Even as a hobbyist, I would be tempted for something like drawers in cabinetry, where there is a lot of repetition. But for recreational building of furniture, boxes etc., I don't get it. And these jigs are pretty darned expensive.
Here's the rationales I see: Production work where time is money High-volume repetitive work, e.g, 24 identical drawers Decorative (I'm tempted to say "gimmicky", but that is a matter of taste) dovetails with contrasting wood layers, unusual shapes, etc. [in another thread, Larry Bud said:] "I can understand why someone would want to cut them by hand, but I don't have the patience or time to learn to cut them equivalent to the quality of the D4."
Are there other appeals to the process of machining dovetails?
BTW, I am not a dedicated Neander, but I don't share Larry's goals of having my hand-cut dovetails look machine-cut. And if I look at $400 for a D4 jig + $50+ for bushings and bits (assuming that a router would not be an incremental cost), I could buy a medium quality japanese dt saw, a set of medium quality chisels (if I didn't already have them), layout and marking tools, and have $300+ left over for practice lumber, which would be lots of fun. And the skills I develop are not subject to limitations on thickness of wood, width or length of workpiece, etc.