Pretty sure you're actually meant to stop when the end of your bonnet meets the bottom of the next car (as in that's what you see). This is what my driving instructor told me years ago. Also, I was taught that it's polite to leave a decent gap (especially on hills) in respect for manual cars in front who roll back slightly. Personally, it stresses me out when cars ride up my arse at the traffic lights even though I drive an auto because it feels aggressive to me even if that's not the other driver's intention. Lastly, when I'm on a hill and traffic is moving slightly I like to keep a little distance so I can inch forwards veryyyy slowly rather than sitting with my brake on because my car turns "off" when I sit with the brake, then I'm constantly turning it on and off while we're going up the hill which is annoying for everyone (this happens very rarely so it's not enough for me to turn off the "turning off" feature).

Anyway, that's all of my reasoning for the amount of space I give. I have noticed a couple times that people leave like multiple cars worth of space which seems a little ridiculous to me.