Great question! I've wondered this myself, and what I've come down to is something like the following:
Having a closet the right size for me -- not too big, not too small.
I will wear almost all the items in it at least once during their season -- although there are always exceptions (e.g. the fancy occasion that does not materialize because the wedding is called off or postponed; the funeral that - thankfully -- does not happen.)
Meanwhile, most items will be worn many, many times per season.
But the amount does vary depending on the specific item, and "wearing the heck" out of a fancy dress or even a pencil skirt, for me, might mean wearing it twice or even once, whereas "wearing the heck" out of my jeans probably means wearing them at least 20 times in a 3 month quarter. That would change if I were working out of the home in a more formal occupation, of course. Then I'd probably be wearing my jeans a lot less and my pencil skirts a lot more. But you get the idea. Because I have more tops than bottoms, I probably wear most tops a bit less often than bottoms, but even there, I have some sweaters that I wear literally once a week in winter time. And winter is long where I live.
I tend to feel uncomfortable or guilty about clothes that I haven't worn at least 5 or 6 times per season, and unless they belong to a special occasion category or the weather has been very unusual (and has thus prevented me from wearing something I had good reason to expect I would wear, when I bought it) then I often get the urge to purge them. At minimum I ask myself tough questions about them, as in, "Did you buy this for your fantasy life?" "Did you have sales goggles?" Etc.
Some items get even more wear. My winter coats, my bags, (I only own a few), my winter boots, my gloves.
I don't really calculate an actual CPW, but I do a rough estimate when I am about to buy something and take that figure into consideration unless it's unrealistic to do so. (For instance, occasion wear will always have a high CPW, but you still need it.) I also try to estimate happiness factor, although that's often more difficult to predict. But something that will give me great happiness even though I won't wear it to the ground may well be worth it to me.
I don't necessarily expect to wear my clothes out, but in fact I do wear a fair number out, after a couple of seasons (or one season, if they are lousy quality). Shoes, frequently worn jeans, knits, and even the odd jacket have been known to wear out on me.
ETA: I notice that for others the issue seems to be not saving their things for "good." I don't have this problem -- but I do think in terms of capsules and my work-at-home capsule is different (though overlapping) with my smart casual capsule for city trips.
