Subdomains (thing.yoursite.com) are often viewed as separate websites by Google. This has indirect implications with many other factors. Matt Cutts called subfolders/subdomains "roughly equivalent" in 2012, suggesting this now happens less, but still happens. Panda recovery stories post-2012 such as HubPages migration from subfolders to subdomains, proves that it still can be a major (subjective) factor.
Source(s): Matt Cutts