It seems to me that there are two distinct phases involved here -- planning and diving. I find the tables or, more exactly, an iPhone electronic version of the tables (for me), easiest to use for planning a dive and what-iffing the scenario. The computer, however, by doing constant modeling of the actual dive, can serve to maximize the dive since few dives are just a vanilla drop to depth, stay at depth, then ascent.
Locally, most dive boat dives are canned scenarios, especially if diving AL-80's. But, given the chance to do something different like larger tanks, more depth, a possible third dive, then going to the tables or the plan mode of the computer, if that's what works for you, is necessary to prevent having the computer surprise you with an ndl warning halfway through your tank.
As far as comments that you don't see people using the tables (which I don't here in South Florida) -- well, you won't see me referencing them either, since I do it at home before the dive.
Finally, I know some see this discussion as beating a dead horse, but given 59 pages of comments, there seems to be a lot of opinion. I think that's a good thing. As a relative minnow to diving, I see a lot of divers with a very casual attitude toward the sport. I am personally very cautious and enjoy taking it seriously and trying to think through various scenarios. A lot can be learned from discussions like this. Keep it up!
-Mike