title: Mongoose difference between .save() and using update()
body: <p>To modify a field in an existing entry in mongoose, what is the difference between using</p>
  
  <pre><code>model = new Model([...])
  model.field = 'new value';
  model.save();
  </code></pre>
  
  <p>and this</p>
  
  <pre><code>Model.update({[...]}, {$set: {field: 'new value'});
  </code></pre>
  
  <p>The reason I'm asking this question is because of someone's suggestion to an issue I posted yesterday: <a href="https://stackoverflow.com/questions/22262114/nodejs-and-mongo-unexpected-behaviors-when-multiple-users-send-requests-simult">NodeJS and Mongo - Unexpected behaviors when multiple users send requests simultaneously</a>. The person suggested to use update instead of save, and I'm not yet completely sure why it would make a difference.</p>
  
  <p>Thanks!</p>