This is an interesting discussion, and made me think about my own diving practices. For me, it's dependent upon the situation. My mindset and demands placed on my buddy vary greatly whether I'm diving an inshore wreck, spearfishing offshore, or now in a cave.
If I'm doing a leisure dive on a shallow wreck (less than 100'), chances are I don't have a buddy nor do I want one. I spend a large amount of my dive inside the wreck and most others on these boats are neither comfortable with my dive plan nor trained for overhead environments. To bring one along for the sake of "having a buddy" would mean every room gets silted out with a high probability of line entanglement - at the very least. If another person on the boat had demonstrable experience in wreck penetration, I may reconsider, but this is not the case 99.9% of the time.
Reef dives vary - many times I'll take a buddy, even if they're a little uneasy. On many of these dives I go into DM mode and keep one eye on them and another eye on stuff to show them. At that point, my fun comes from their fun, and I'm assuming a mentor/leader role. If there is another diver on the boat with similar experience and comfort, I will make an effort to pair up with them in either a standard buddy role or a same ocean role (which may even switch mid-dive). If I'm diving with another pro, I will probably take a lot for granted, and assume they share the mindset of self sufficiency. I will help them if I can, but I will allow them the freedom to dive how they wish to dive. I will make suggestions and discuss gear, mindset, etc... but often this does not alter my dive plan unless a red flag is raised - we all know arguing with most dive instructors is an exercise in futility.
If I'm spearfishing - it's exactly like DD brings up. When hunting is involved, all rules seem to go out the window. In this instance, even if I'm with someone - I'm psychologically solo diving. I'll help if I can, and I'll point out stuff that doesn't look right, but once you splash it's every man for himself. I pack my own pony and O2, and am usually the only one to do so.
Over this week I received my intro cave card, which has had a huge impact on my mindset. The demands placed upon you in that environtment allow zero tolerance for errors and malfunctions. It was both refreshing and totally enlightening to understand what it meant to be a dive "team" - something I've never had the pleasure of experiencing. In this instance, just as the environment is zero compromise - so must every team member be. An equipment failure is a called dive until resolution, period. Same with a psychological inhibition, and it's the responsibility of every member of the team to ensure 100% operation of every member's equipment and psychological status at all times during the dive. In this instance, I'm not only ALWAYS diving with a buddy, but I'm constantly evaluating his equipment and mental status because my life could easily depend on it. For that reason, I'll never berate someone for calling a cave dive - chances are, I'll be that guy someday as well. (The take-away: carry a HUGE save-a-dive kit
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