The safety must be taken into account, especially when an accident/collision occurs. During accident, the occupants will be 'thrown' to the front. Let's consider these scenarios :


1) Kid/Baby facing front in car-seat
- Force will be on the kid's front, specifically where the seat-belt is.
- Head (which is much heavier in ratio) will be thrown to the front. On top of this, a baby's neck muscles are not fully developed, and may hurt.


2) Baby lying down
- Need to study the seat-belt structure and how it straps the baby


3) Baby facing back in car-seat
- This is recommended, as during collision, the force will be on the baby's back.
- Check out EU's recommendation for clearer explanation

IMHO, it is both for safety an convenience.

Why safety ? If one installs the s.belt wrongly on the car seat, it is as good as not having the s.belt


It is was me, i would not use the ISOFIX. Just use the normal baby car seat using normal s.belt. You can easily transfer it to other cars and pass-it-on to others. Baby/Kids grow fast, and mine out-grew it within 8 months.... In other words, More practical.