I was was a Brooks Brother customer for decades and that firm trained me to be fairly casual when ordering clothes. They had their own way of doing things and one need only choose a cloth, specify single or double breasted and wait until the garment was complete.
That casualness ended on Savile Row. My first tailor there was another of those institutions that had own their way of doing things, accompanied by an unfortunate tendency to make single breasted suits when they had been asked for double. And the reverse. Needless to say, their casual approach brought my casual approach to a quick end.
And though considerable time has passed the need for specificity is still with us. Take covert coats, for example. Coverts have been around for a century or more and most men would assume that that their design is standardized. Just specify the collar and be done with it would seem reasonable, but that is so untrue. For example, the rows of stitching along the hem and sleeve ends that were designed to keep the coat from fraying when riding through brush. Order a covert expecting authenticity and one is likely to find that the stitching has become purely decorative, and invisible from a few feet away.
Coverts are also known for their interior game pocket, a space inside the left side lining that is perfect for storing a scarf (who among us has not lost scarves that were stuffed into a sleeve at a coat check?). But leave the pocket unsaid and it is likely to be left unmade. There may be more, but two complaints should suffice.
Now one cannot blame one's tailor for a failure to read the customer's mind. And the cost of imperfect communication is only the couple of months that it takes to return a garment to the shop for changes. But that delay does mean that an item is likely to be delivered at the end of its intended season, relegating it to storage for half a year before it can be enjoyed.
And that is a very good reason to always be specific.