Decanting is cheaper than buying travel sizes and stops you carrying three-quarters of a shampoo bottle around the world.
Our bottles and dispensers are sized to airline liquid limits so they clear security without discussion, and they seal properly — the failure mode with cheap ones is pressure change at altitude, which is how a bag ends up full of conditioner. The cream jars and pump bottles cover the things that don't pour.
Pair them with a clear wash bag and the liquids part of packing stops being a consideration.