Hand-tied wefts are usually more expensive because they are more time consuming to create. These wefts are lighter, thinner and less rigid, making it more difficult to install when doing a sew in. The trade off here is that hand-tied wefts lie extremely flat on the wearers head making blending a breeze. Also if you have thinner hair there is less chance of having the peek-a-boo effect where your hair separates or moves and part of the track becomes visible.
Because the tracks lie flatter some would argue that sew-ins done with hand-tied wefts are more natural looking. I think that is a matter of opinion and what your desired look is. Because these wefts are a bit more delicate and do tend to shed more especially if you need to cut them. Sealing the hair is absolutely necessary and you should avoid cutting the tracks whenever it can be avoided to prevent excess shedding.