I'm very unlikely to buy a size that won't fit me or my immediate family members. But somehow, no clothing shop seems to allow you to set up a couple of profiles (women's clothing size M, men's clothing size L) and filter the entire catalogue by default.

I'm reminded of the highstreet, where I've only found one shop that sorts clothes on the rack based on size. I suppose this is to encourage browsing and inquiring if your size is 'in the back', but it's excrutiatingly inefficient.