Most of my knives get reprofiled but I rarely go below 30 inclusive. Not because I don’t like thin edges and not because I’m afraid of damage...just because I’m too lazy. I like using the Sharpmaker so 30 degrees is a convenient angle to work with. Most golden and seki knives come close to 30 from the factory so I usually don’t reprofile them until my microbevel becomes invasive. Most of my Taichung folders have come with a very obtuse edge (between 40-50 degrees) so all of my Taichung knives get reprofiled immediately. It always kind of amazes me that a maker who holds such incredibly tight production tolerances can’t sharpen s knife to 30 degrees like the rest of spyderco’s factories.
Anyway, I have a couple of knives (including a Millie) that I have reprofiled to 20 degrees with a 30 microbevel. They cut well, but honestly, you need to regrind the primary bevel if you want to see more marked differences in cutting efficiency. An axe with a 20 degree edge will cut better than an axe with a 30 degree edge...but it’s still going to cut like an axe.
Regarding how thick we really need our edges, I’ll offer this example. I usually freehand my fillet knives to 20-25 degrees inclusive. Those knives are less than 10 thousandths behind the edge and sharpened to 20 -25 degrees and spend their lives cutting through hard scales and fish bones and banging into a hard cutting board over and over. I can’t remember EVER having any significant edge damage. I can’t speak for how anyone else uses their folders but for me, that data proves to me that most folders are ground WAY thicker than what I need to prevent damage, even in my hardest use scenarios.