With soft structured baby carriers, young babies who can't hold their heads firmly must be carried in the front because we need to constantly monitor them and make sure that their heads won't slump forward, restricting their airways in a chin to chest position.
However, bigger, and heavier babies can block their parent's front view and tilt their balance forward. One of the main reasons for ER visits in the US, with cases related to baby carrying, was parents who fell, usually tripped, with their baby in the carrier. The data is open to the public in NEISS (the US National Electronic Injury Surveillance System). Moreover, when babies are carried in the front, especially forward-facing, they are more exposed to getting injured or burned.
Therefore, as your baby grows, especially if you are in motion, both indoors and out, the back carrying position might be safer than front carrying for both you and your baby (and more practical and ergonomic ).