In the UK I think they're all of those things, to be honest!
They're certainly worthwhile unless you can find a friend or relative with an enormous amount of patience and trust to teach you, as driving certainly isn't something you can teach yourself.
Ideally you should have a mixture of both, so you can have a bit of practice in between lessons.
noeusuperstate - "Anyone earning less than £10k a year in the uk aged under 21 would spend nearly all their income on it" - I disagree. Remember, most people of that age group (17-20 year olds) are still living at home with their parents - you can easily run a car on min wage if you don't have rent and household bills to worry about!
"If you can manage without a car until you are in full time employment and earning about £20k pa" - well, on average, most people in the UK would not own a car until they were in their late 20s or 30s if this was the case. Depending on where you live (e.g. city or rural area), it may not be practical to go without a car for that length of time - having more money to spend on "clothes and leisure" is not much good if you can't easily go to places to buy clothes and spend leisure time.
Also, even if you don't own a car (which I didn't, for many years) it's still nice to be able to rent one when you need one, e.g. on holiday.