The reason for soaking raw denim is only in part to get the shrinkage out, it is also to bed in the constructional threads, if you do not soak raw denim prior to wear you will reduce the life of the garment…...So yes, of course no "must" just seems a little silly to me to reduce the life of a perfectly good garment....
"Bedding in the constructional threads"–I had never thought about this aspect before. It seems extremely important in hindsight now. I may go ahead and soak my raw workshirts now.