fusible interfacing can be useful , but you will find very few professional tailors making quality garments who use it much or often.It does have a place of course, and it can be useful, but you will find that a hand stitched interfacing allows greater shaping, or adding different layers and weights, and actually it's often easier to hand stitch smaller pieces than using the iron on stuff.
Realistically it is a shortcut, and whilst the "heat glue" has imporved over the years , it can delaminate over time or washing.
If I am spending a relatively large amount of money on fabric, I'm going to making the garment in the best way possible, and that still remains using non fusible interlining