One of greatest advantages of node is a block-less environment.  Better described by the node.js wiki:

Node.js is primarily used to build network programs such as Web servers.[43] The biggest difference between Node.js and PHP is that most functions in PHP block until completion (commands execute only after previous commands have completed), while functions in Node.js are designed to be non-blocking (commands execute in parallel, and use callbacks to signal completion or failure).[43]

This non-blocking feature is ideal for real-time updates like chat rooms and social media.