Since many people already have accounts with these popular websites, it makes it very convenient for them to quickly log in and access the full functionality of the review site without having to create an additional account on that review site. Or at the very least, it makes account creation for that website a little more simplified.
We feel this is a very important feature because people are more inclined to leave reviews on a review site when it is hassle-free. Any added steps could deter them from leaving a review altogether.
What are your thoughts? Do you think that alternate logins are a great feature? Let us know in the comments below!