There is only one way to log into Tinder and that is through a Facebook account. No Facebook account, no Tinder. Supposedly this is for security purposes but really that is a poor excuse as anyone can make a fake Facebook account.
OKCupid has sorting options for its matches such as distance or compatibility, this allows for users to easily find the kind of matches they are looking for.
This integration allows for the app to hook you up with mutual friends based on your Facebook friends list. That means that you won't meet up with a totally random stranger.