I have a twin sister, and our mother did this to us until we were 12, she had a pink version of all my clothes. I hated it as a kid.
But now we still do it sometimes, if we're hanging out together we coordinate outfits, Halloween costumes, Christmas sweaters, everything. For our 18th we got matching tattoos, and we wear matching silver necklaces.
Yeah, we are pretty dorky. but I'm not so annoyed with our parents dressing us the same anymore.