I'm having trouble getting my 10 month old DD to sleep without being fed and in desperation I decided to put her in her car seat in her room to see if she'd settle as she settles so well in the car.
So she was crying for the time it took for me to have a wee and then just stopped.
I carefully open the door to her room to find her sitting next to the car seat! 
I obviously would have pulled the straps tighter if she was in the car but I've definitely seen people have the straps as tight (or loose) as I'd done it today.
That's really quite scary how easily a child could be flung from their seat. 