Hi Rosevb,
When a person who has PAID her money to learn and get certified in how to dive, comes on an internet forum and asks this question then it reflects the pathetic state of scuba education being given to recreational divers. I too have come out of scuba diving courses wondering exactly the same thing. Now that I am certified, how do I really do what I am certified to do? The question is not whether you should dive with a computer or without one. People can have their opinions on it and there is no right and wrong answer. The real question is that as a certified diver, we should be able to determine that for ourselves.
When we are teaching a new student basic arithmetic, (2+2 = 4) are we training them to do that on calculators from day 1? I do not know of any school that teaches basic math by handing students calculators. It will reduce the time schools spend on each student considerably but we are still teaching numbers then basic 2 -3 digit math. Speech software is turning spoken word into written letters. We are still teaching words and alphabets. Scuba industry unlike public schools is profit driven, therefore basic common sense that applies to all academic scenarios is abandoned so that gadgets could be sold. You will never see commercial diving schools or military diving academies training divers on computers from the first day even though they are training professional divers. They all start out on tables and every diver diving in professional capacity is able to conduct their dives using tables.
By using tables for the first few dives, a student has demonstrated that she has the understanding of what is happening inside a computer. If computers were taken away from divers today and they were asked, "Do you understand what is happening inside this gadget? Can you show me?" A person who knows that is happening inside the computer will be able to take NDL limits, how they turn into repetitive dive groups and be able to show you what a computer is actually doing. You can be sure that now this person understands decompression. There are so many divers who will not be able to show you what is a computer doing on some of the most basic dives and yet in their own minds they are convinced that they understand how decompression works?
When we create a culture of starting people out on dive computers from the very first day then we end up creating a very large community of grocery shoppers who will go to the grocery store with a 10 dollar bill, pick up 4 soda cans of .99 cents each and then pull out their cell phones and add this up to know if they can afford the purchase or not. Then they will say "In the age of calculators, life has become so easy. Too bad that some people are still living in the antiquated times where people were taught how to do REAL MATH!"
Trust me when I say this, the real world situations I have seen in diving were far far more idiotic than the imaginary example I just gave. I would suggest, sitting with your instructor and throwing questions at him for which you are confused. If the man does not make sense then it is not because you are slow to learn. It is because you just have a very bad instructor. I would find someone else.