Is mass linking (the same link) from subdomain to main domain bad? A business has a subdomain for a separate service. That subdomain has lots and lots of results pages. Every one of those results pages has a link directly to a page on the main domain (all links go to the same page), is that going to negatively impact the main domain in any way?
No, there is no issue, although it becomes a good because your internal linking would be strong and link juice pass to every page.