title: Redis is thread safe , so why use `BlockingConnectionPool` in redis-py
body: <p>I use Django cache.I know Redis is thead-safe. </p>
  
  <p>If <code>BlockingConnectionPool</code> is necessary, when I configure <code>CACHE</code>. </p>
  
  <p>What does <code>BlockingConnectionPool</code> do?</p>
  
  <p>When I need use <code>BlockingConnectionPool</code>?</p>