I wash fabrics to get the sizing, smells and fumigation out of them as I have allergies that are triggered by that stuff.
However, I would wash fabric whether I had the allergies or not. Here's why:
Most quilt shops are in some kind of shopping center. The quilt shop may be spotlessly clean (at least the parts we see), but the other shops in the store may not be. Since most of the shops in a shopping center share walls, plumbing pipes, heat/AC venting and roofs, lots of unwanted critters from less than spotless shops have EASY access to the spotlessly clean shops.
So I wash fabrics when I bring them home. Unless I am going to use them right away, I fold them right out of the dryer and put them away. They are ironed right before I use them.