But, brick & mortar stores rarely have clothes that fit me* AND I somehow end up between sizes, so I tend to order two of everything (in S and M, or whatever) and return the one that fits worst.
From an environmental standpoint, I have no idea if this is better or worse than having fully-stocked brick & mortar shops. But, fact is, those don't exist any more, so this is what I do.
* At 5'7", I'm slightly on the short side for an American male, and at 150lbs, I'm smaller build than most as well. IME, clothes are either cut for skinny teenagers or for dads with 38" waists. And I'm neither, leaving to try on and return many items.
Edit - since maketheman's post got killed... I've yet to find a clothing brand that lists thigh or arm diameter, which tend to be the problem. The "slim-fit" stuff you mention usually fits my waist or torso, but will not go over my bicep or quad. And the normal cut from the same brand fits like a trash bag. I'm fine getting tailored clothes for suits and suchlike, but I'm talking about jeans and casual shirts here. Anyway, it's a totally first-world problem to have, I can deal with it.