Or, in plainer words, 'removing the ovaries' vs 'removing the ovaries AND uterus'.
Here are two studies talking about the benefits of this (much less invasive) type of spay (ovariectomy): Study 1 and Study 2.
It sounds like a win-win... less invasive and (I would assume) quicker recovery time for the dog. I've heard arguments against ovariectomy, but those studies seem to show that there is actually not a higher chance of health complications because of it.
Ovariohysterectomy is the most common type of spay in the U.S., but I would hope that knowledge of the alternative could help people make the choice for the other surgery if it was appropriate for their dog.