They must have changed this as late last year I booked a car for a couple of days whilst in Las Vegas and then went elsewhere for a few days before returning to LAX.

I've been looking at car / hotel + flights and you're forced to book for the entire period now.
Not useful if, as above, or you're in LA for a couple of days (so just need a hotel for those nights) and then want to drive up the coast stopping off at various places. You're forced to book everything separately.