What kind of practical difference does legalizing make?
laws can be passed to allow retail locations to open, so you can get weed from a dispensary instead of a dealer. cops can't arrest you for possession as long as you follow the rules (see below). those seem like 2 pretty big differences vs. the current state of play.
You can’t drive while smoking a joint? Can you be in a moving car? Parked car? Walking down street?
i can only speak about WA, but: no, neither driver nor passengers can smoke and drive. parked car OK as long as you're on private property, you can be fined for public consumption. no walking down the street while blazing for the same reason.
alcohol is a good proxy for a lot of such questions: if you can't do it with booze, you probably can't do it with weed either. not a perfect 1:1, though.
Do cops usually enter your house to make sure you are not lighting up?
state and local cops cannot enter your house if they only suspect you have a personal amount of weed, because it isn't a crime. if they are in your house for some other valid reason and see that you have weed, they can do exactly nothing about it. here's a trip: get arrested in WA, you're hauled down to jail, you appear in court, are given a date for your trial, you post bail, and on your way out of the courthouse the cops will give you your weed back.
feds obviously take a different view, but i don't know of any DEA agents banging down doors to arrest weekend joint smokers.
folks on the right joke that cops will bust down your door to ensure that you ARE lighting up...