Asking out of curiosity, but by any chance is the buddy someone who is new-ish to the GUE system? I ask because in Fundies class GUE teaches you to pre-plan and then dive with the computer in gauge mode. They teach that because, as others have already mentioned, they want to wean you off the idea of "flying the NDL"--letting the ever-changing number on the screen dictate when you turn your dive. The strict use of gauge mode is more of a training tool than anything else. From what I have seen, there are some really experienced GUE-trained divers who keep their minds open to their computers' full capabilities--they just don't let the numbers on the screen override what they have already planned. Rather, the computer backs up or complements what they planned.
Planning shouldn't be onerous. A computer's planning mode can be used to pre-plan a dive. In advance of the dive, you should have at least a rough idea what you would like to see and the route to get there and back--it's not a great idea to go willy-nilly from one place to another and another on a whim, especially if these are cavern dives you're talking about. You should have at least a rough idea how deep the route and destination are. Based on the depth, you can go into your computer's planning mode and see how many minutes you can spend at that depth, or the average depth if you prefer. If you know that time limit in advance and plan to adhere to it rather than "fly the displayed NDL," there really isn't much point to restricting your computer to gauge mode on the dive.