Fusible Cons can wrinkle or dimple even

Fusible Cons can wrinkle or dimple even if you fuse it flat and correctly.
It can drastically change the drape of the fabric (sometimes this matters, sometimes not so much.)

Sew-in Pros:
Easy to go back and cut excess interfacing from seams to reduce bulk.
Adds thickness, stiffness and stability to the fabric without completely changing the behavior of the fabric.
Does not leave wrinkles or dimples like fusibles can.

Sew-in Cons:
Does not make fabric easier to feed through the sewing machine.
You will have more layers to keep track of and line up, oh and pin. (I hate pins… I’m enjoying the new Clover
wonder clips instead.)

There are 4 main types of interfacing:
Non-Woven Sew-in
Non-Woven Fusible
Woven Fusible
Woven Sew-in

Fusible Pros:
Makes the fabric thicker or stiffer.
Stays in one place and does not shift.
Stabilizes the fabric and make it easier to work with.

http://www.interlining-factory.com