title: Creating multiple instances of PhantomJS or only one?
body: <p>I have a script which needs to crawl a website. For every request(each URL), I initialize a new web driver with selenium/phantomJS .
  Is this approach unscalable and will it cost a lot of CPU usage over time? 
  Should I rather only create a single driver and save it somewhere in a global variable and reuse it for all the requests?
  Will doing this lead to lower cpu usage or won't be much effective?</p>