title: when to use `mongoose.disconnect()` or `db.close()`
body: <p>I am new to MongoDB. Now I am using Mongoose to take care of the database in my express.js app. My question is that I don't know when should I close the connection? Since someone says better to close it, while someone else says to leave it open? And what is the difference between <code>db.close()</code> and <code>mongoose.disconnect()</code>? What is your experience of using these? </p>
  
  <p>Thanks!</p>