I obviously do not know what Luca was talking about either, but these are my thoughts as a "personal stylist". Tailors can give the best technical advice about a suit - for example, is a particular cloth suitable for a specific kind of suit. However, tailors are craftsmen. In my experience, they are not that interested in fashion, in the broad sense of the word, and they are used best when the customer also uses the services of a stylist. In the case of a company like Rubinacci, they have tailors *and* stylists in house. Mariano and Luca, and I suppose anyone else who works on the fittings - these guys supply the taste levels, and the actual cutters, they actually make the stuff - they are the literal hands of the operation. When you go in to do a custom suit, usually, about 90% of the options are already set, and you just have to make fabric choices, give guidance on how you like things to fit, and make choices about cosmetic details. Too much choice is not freedom, it's chaos. And besides, a lot of those choices are opaque to the customer, and make no sense unless you have a technical background anyway - the type, gauge, and color of the thread to use on the seams, on the button holes, the material for the interlining,etc... However, it's my experience that someone is often needed to help most customers make those last 10% of choices.
One MTO from No Man Walks Alone illustrates why this is a good idea. So, at the trunk show, Greg did MTO with Inis Meain. Solid yarns are pretty easy to figure out. If you choose a navy yarn, you are going to end up with a navy sweater, you hope. However, you introduce a marled yarn, and how that will turn out depends a lot on the stitch type. If a large part of the sweater is going to be done using simple purl stitch, you are probably going to end up with a camo effect, the size of which depends on the yarn being used. If you use a rib stitch, with are alternating lines of purl and knit stitches, you are going to get less of a camo effect. And anything complicated, like a cable, is going to drown out most of that effect. I doubt that many of the people ordering had any idea that this was going to happen, and how a particular yarn would look on specific models. That's where an experienced stylist comes in handy. For a tailor, if you are going beyond, say, your basic blue and charcoal flannels and worsteds, it's a good idea to work with someone who has high taste levels, understands your preferences, and can also help you communicate with the tailor. It's not always easy to know what a suit is going to look like from a little swatch of cloth. Incidentally, this is one of the reasons I advocate RTW+ alterations for most people, or having something copied with few or no changes. Bespoke, even with the use of a good stylist, is a rich man's game. You are nearly guaranteed to strike out some of the times. That can get costly, fast. With RTW, you know right away if you like something, and a good alterations tailor can get something that looks good to begin with, look really good with alterations. The same goes with every other sort of commission - shirts, jewelry, footwear. Edward Green limited their mto options couple of years back, probably to avoid the dual problem of disappointed customers and Edward Green branded crazy shoes walking around in the wild.
The worst results usually occur when an inexperienced customer with mediocre to poor taste levels decides to take it upon himself to be both the stylist and the tailor. The biggest complaint that i've heard fom tailors is a customer coming in wanting to do CMT with a cloth that is unsuited to the suit that they want to make, which is in turn a poor fit for them, no matter how to cut it. tldr; I agree completely with @edmorel - added an example, rambled a bit.