It depends. Usually my daughter will fall back asleep after I get her out of the car seat
If she slept less than say 30-40mins of the journey and I know she's going to wake up grumpy and tired I will hang out in the car if I'm not in a rush. Sometimes she wakesnup herself when the car stops or if we have somewhere to be i just grab her out
If we're going home, I let him sleep when we get there. If we're going out, it's hard for him to sleep if he's not consistently moving. If I go out, I don't really have time to just sit in the car, as much as I hate interrupting his sleep.
Depends on how long they've slept and if we are in a rush really. If no rush then I'd let her sleep but only up to an hour