There's a minor issue with your proposition there, buddy old pal old friend. You see, if you just auto-heal then there's no risk of you forgetting to heal. If you never have to manually heal out of combat, you never have to worry about traps unless for some reason the traps or barriers are gonna auto-kill you, which is usually considered bad game design.
Therefor, always being at 100% HP out of combat is a bad idea because it removes challenge and strategy from a large number of things in the game. Such as back-to-back encounters, or traps.
