Folding the tracks reduces the amount of shedding and helps maintain the integrity of the wefts making it easier to reuse. The only con that the install maybe be a little bulky especially around the leave out. The amount of bulk is dependent on how thin the wefts are (single or double wefted) and the sewing technique.
As for cutting the wefts...this is beneficial if you want a super flat and versatile install. The cons are that the wefts will shed more and the weft pieces may not be reusable.
When I did get sew ins, I preferred a combination of both. Flip over method on the back and wefts cut closer to my leave out.