Many of you know that 85% or more of my diving is solo, and I do 250-300+ dives a year. Solo diving is necessary for me for many reasons. First, most of the other divers on the island that I enjoy diving with are professionals and are tied up in work-related diving. Second, diving is "work" for me... I need to do it, and do it frequently, to acquire the video footage for my cable TV show, DVD's and stock video sales. Diving with a buddy who is not attuned to the needs of my imaging can ruin a dive for me by ruining any chance of getting footage... due to sediments being stirred up, feet or fins gettinbg into my frame, bumping me while filming, etc.
I have 46 years of diving experience, much of that solo dating back to the mid-60's. I dive with redundant equipment (well except the brain, but I am a Gemini). I do take calculated risks (for example my deep diving) that I would not subject a buddy to.
However, I do NOT and hopefully never will advocate solo diving for anyone else. It is just not my call. That is a decision that needs to be made by the diver and those familiar with their diving. There are very few divers whose skill levels I can validate. More importantly, there are even fewer divers whose mental readiness I can evaluate.
A diver deciding to dive solo should (IMHO) have enough experience to know two primary things.
First, their "normal" response to narcosis. I am one of the lucky ones who is certainly affected by narcosis at depth, but very able to function effectively (as attested to by the footage I shoot down there). Oh, occasionally I get narc'ed enough to think I'm seeing a lovely lady beside me... but I'm not taken in enough to follow her down past 200 ft when she beckons!
Second, a diver should know how they respond to sudden emergencies such as equipment failure. Although that has been a rare occurence in my 46 years, it has happened on a few occasions. Each time I have remained clear headed, not panicked, and addressed the problem calmy and overcome it.
So I won't tell anyone else they should dive solo. There are many benefits to team or buddy diving... the added safety margin and the ability to share the dive both during and on the surface interval for example. I love sharing my dives with my regular buddies when they can join me.
If one chooses to dive solo, I will comment on certain aspects. Working on the dive boat I have seen a number of solo divers who just shouldn't be doing it. For example, several times I have seen divers descend beyond recreational depths with no redundancy at all. This is just asking for it. The one time I decided NOT to strap my pony onto my primary tank because I only planned to go to 40 ft was one of the two times I actually needed the pony (due to the tank valve becoming clogged and delivering no air, period). I stress the need to dive redundant to them and offer my experience as one good example of why this is necessary. I see divers who have fewer than 50 dives going solo. I also think that is ridiculous (although I was guilty of doing the same... in a day and age when dive buddies were rarer than hen's teeth).
I rarely tell anyone else how they should dive. I prefer to tell them what marine life they saw on their dive (assuming they give me a good enough description). That's what I'm trained to do as a marine biologist... and I enjoy enhancing the dive experience of others, and helping them to gain a better appreciation of the marine life whose environment they are entering.