"Autism Spectrum" is a deliberately vague term that has been created and stretched to bring a variety of minor social and emotional functional differences under the general label of "autism". As far as I can tell, in the US the major purpose of this has been to divert special education funding from severely impaired children to less-impaired children from higher socioeconomic strata, and it has been very effective in doing so.

So to directly answer your questions, "Asperger's" (or whatever substitute term you find acceptable -- I'm perfectly fine with a substitute) is very useful to distinguish people with minor social and emotional functional differences -- those people who are, for example, able to hold down a tech job and post about autistic politics to Hacker News -- from highly impaired people such as my daughter who will never hold a job and whose verbal skills are at a three year old level.

These distinctions are vitally important to ensure that appropriate funding goes to these highly impaired children rather than being siphoned away to children of well-connected or politically savvy parents who are fully capable of succeeding in the mainstream educational system without aid.