Is there any benefit to using WPA2-PSK instead of an unencrypted network? Oh yeah, you better believe it! There sure is. There's a massive benefit: anyone who is not authorized to use the network cannot eavesdrop on connections, send packets over the network, or modify packets sent over the network. That's huge!
Look at it another way: There might 100 authorized users, and approximately 5 billion unauthorized users; narrowing down the number of people who can attack your connections from about 5 billion to about 100 is a significant win, particularly if you can control who those 100 are.
(If that's not the question you were asking, please edit the question to clarify what you were asking.)