title: Why "bundle install" a gem instead of "gem install" for a rails 3 app?
body: <p>I'm a beginner programmer going through the <a href="http://ruby.railstutorial.org/chapters/modeling-and-viewing-users-two#fnref:7.13" rel="noreferrer">railstutorial</a> by michael hartl, and notice that the process for using gems in the application is through adding it to the gemfile, and then doing a:</p>
  
  <pre><code>$ bundle install
  </code></pre>
  
  <p>Any reason why one wouldn't just do a:</p>
  
  <pre><code>$ [sudo] gem install [the_gem]
  </code></pre>
  
  <p>and then just add it to the Gem file? I know this was somewhat the process back in rails 2. </p>
  
  <p>Thanks!</p>