Sometimes when I'm someone's guest or playing a new course that requires carts I frequently even offer to pay the cart fee but walk.
It's very rare they allow this. So basically I throw my bag on a cart and end up doing a lot of walking anyway. Walking from my approach shot to the green, walking from green to next tee, etc. Particularly if it's with a friend or relative who I know doesn't mind that. In a way it's nice, I get to walk but without having to carry my bag.
My complaint with carts is that people don't know how to use them optimally. I live on a private club and see it out my window all the time (I work from home so I watch the 7th hole at Harbour Trees all the time).
Cart partners' balls will be 20 yards apart. Driver will drive up to the first ball. Get out, do his preshot routine, hit his ball, clean his club, get back in his cart and drive 20 yards to the other ball and let out the 2nd golfer. Then he will do the same thing.
What should have been 15 seconds, max, between those two balls being struck is now probably 90 seconds or more.
If they'd have been walking they'd have hit their shots 15 seconds apart.
On many courses with tees close to greens, I really don't believe carts speed anything up, and often times may slow things down.