If you simply drop to some depth, stay there and return to the surface, then tables are fine. But if your dives are more varied, then using tables and getting max bottom time is a lot more difficult. I did a dive the other week that violated the heck out of any table but was in fact fine. We were diving in a cavern and dropped to about 35ft where my buddy and myself had some equalizing problems. We had to linger at that depth for a several minutes while our ears cleared, we then proceeded to about 95ft for several minutes and finally returned to 20ft for at least 30 minutes. We had plenty of gas so we decided to hang around at that depth and do safety drills. The max time by the tables is in the 20 minute range, our actual time was 59 minutes but at no time did we go into deco, did not even get close. Had we been using tables only, our dive would have been cut by 2/3s. These multi level dives are typical for me.
I don't buy the "rot your brain" argument. No doubt there are "divers" who would totally forget the tables but I suspect they will anyway....you know--jump in, follow the guy next to you style diving. These "divers" are not going to use the tables no matter, at least a computer MIGHT help keep them safe. Then there are others, myself included, that use a computers but I refer to the tables as well. I know the NDL times and can use tables if I need to. Add NITROX to the equation and the computer add a lot more value.