title: When to use a key/value store such as Redis instead/along side of a SQL database?
body: <p>I have read great things about key/value stores such as Redis but I can't seem to figure out when it's time to use it in an application.</p>
  
  <p>Say I am architecting a web-based application; I know what stack I am going to use for the front-end, back-end, database(s), etc..what are some scenarios where I would go "oh we also need Redis for X,Y, or Z."</p>
  
  <p>I would appreciate node.js examples as well as non-node.js examples.</p>