I have always prewashed since I was growing up with a seamstress mother. When new fabric finishes came along,
some of my children reacted to them if someone gifted them and had not prewashed the item before.
My most sensitive son has now developed many food allergies in middle age too.
With as much laundry as I had when all four kids lived at home, prewashing did not take much more time then. Now it is so much easier with most kids gone.