Listening to F/O's approach briefings they always deducted RESV fuel from arrival fuel and declared they had X minutes holding fuel in hand. When the weather is bad they did not include things like a G/A and 2nd approach and then divert: did they have enough to do that? Something to think about. They didn't reduce calculated holding time BEFORE declaring a diversion to allow ATC to coordinate the diversion. In some areas I've had to wait 5mins for a diversion clearance. There's also the coordination with the company to consider. If there is a choice of diversion which do they prefer. If you all go to the same place will you re-fuel and fly again, or bus the pax on buses that don't exist anymore? Entering an area with TS, or Fog, or any other cause for a diversion I'd have every option airfield's Metar written down and a priority list decided upon BEFORE entering the lion's den. I always declared a decision time when reaching destination in bad weather. Capt's who've never diverted might never have benefited from the thinking and deciding process, so when it is their call they are learning as they go. Amazingly F/O's in some companies report that their command courses did not include class-room discussions about such scenarios. It would be wonderfully useful education to have group discussions about what you'd do if...... and what thinking process and variety of considerations come into play. A/C with no method of contacting company directly, or operating into an airfield with no radio for the handling agent need a captain with a wise head and that often comes from having seen it done before. If captains have not diverted it is likely they've not done a G/A from minimums. I remember my first one as an F/O; it was such a surprise and amazing, especially as I saw the approach lights whistle under us as we climbed away. Before it had been just a sim exercise. Having done it the mystery was now clear. Once I'd seen an ace captain do a G/A from a CAVOK visual circuit the lesson was learnt. I was fortunate to have had a sound apprenticeship. That is lacking in todays rapid promotion process.