I did my first dives after certification nearly a quarter century ago in Cozumel, where the law requires you to follow a divemaster. I just pulled out my first log book and saw that my first non-training dive was on Santa Rosa wall, diving on air to a maximum depth of 90 feet, with a bottom time of 38 minutes--that does not include the final ascent and safety stop. Back on the boat, I pulled out my log book and tables so I could do exactly as trained--calculate my pressure group and prepare for the next dive. I saw then that my maximum bottom time according to the tables was 25 minutes, so I was completely off the tables already. What should I do? I looked up and saw everyone else on the boat looking at me with bemused smiles. One of them pointed to the tables in my hand and said "it makes a decent Frisbee."
So I finished the week blindly following the DM and trusting he would not get me bent. As soon as I was home, I bought a computer.
A few years later, again diving in Cozumel, I went with an operator (Aldora) that required computers on its dives. They were using steel HP 120 tanks, and it was not unusual for them to do dives to 90-100 feet or more that last over 80 minutes. I always did them on EANx 32, but there were many on air. In fact, in the first years I dived with them, almost everyone used air for those deeper dives. You could do dives to that depth and that time and still stay within NDLs because they were multi-level dives, and everyone was using computers that could deal with multi-level dives.
Earlier in this thread, Mac64 said that any multi-level, NDL dive could be planned using tables or the rule of 120. Challenged to do that, his solution was to have the diver use EANx 40 in violation of standard PPO2 limits and treat it as a flat profile dive. Even a EANx 40 dive to 100 feet has a limit of about 40 minutes on PADI tables. He never once showed how to do a multi-level dive using tables.