I do not normally wear helmets except those that I pick up when a mob drops them since I do not need the extra protection, plus they are a bit of a waste of diamonds and XP due to their low durability (not that I have any problem getting enough of either, and by putting Protection IV on my chestplate and leggings I spend more XP to repair them for less average protection than full diamond armor, but more against sources like fall damage).
As you can see here I'm wearing a gold helmet, then a chain helmet with another leather helmet (enchanted) in my inventory, both picked up:
The last time I checked, I'd gone though more than 250 gold helmets alone, giving you some idea of how often they are dropped (not very considering that I've killed 140,000 mobs, mostly hostile, and around 2/3 of them zombies and skeletons. I've still managed to get them often enough that I've crafted more than 80 by combining two worn-out helmets before the first one breaks, so I've gotten closer to 330). I'll sometimes even combine enchanted helmets in the anvil. I do have a diamond helmet with Aqua Affinity and Respiration III but I only use it when working underwater, like when digging a railway (at y=58, so they often hit water); if a mob ever drops a diamond helmet I'll keep it as a trophy, like the leggings a skeleton dropped a while back, and a chestplate dropped by a zombie much longer ago (the chestplate has Thorns so using it to repair the one I wear isn't an option anyway).
I guess that makes sense... I understand now... because boots have more durability while costing less than a helmet, and that stuff and stuff blah blah blah.