I know that we have synchronized transmissions these days, that double clutching used to be necessary but now is not. But I don’t know if it’s beneficial at all.
My first 300ZX used to crunch sometimes when moving to second and fifth. I started double clutching and it stopped happening, so to this day I double clutch on every shift. I guess that means the synchros were worn - which implies double clutching might prevent them from wearing. But perhaps depressing the clutch twice as often is causing more wear on the clutch to counter-act that - I don’t know.
There’s a lot of misinformation on these topics. A combination of older folks who had techniques like this beat into them but never understood why, and people who preach things because they sound right with no formal evidence whatsoever. Much like people who tell you to engine brake to avoid wearing the brakes which is laughable.
What say you Oppo?