title: Why is changing constraints in updateConstraints faster than at other times?
body: <p>I have read <a href="http://oleb.net/blog/2015/08/how-to-use-updateconstraints/" rel="nofollow">this article</a>. It states that Apple gives some advice about using the <code>updateConstraints</code> method. The part that confuses me is as follows:</p>
  
  <blockquote>
    <p>It turns out that changing a constraint inside updateConstraints is actually faster than changing a constraint at other times. The reason for that is because the engine is able to treat all the constraint changes that happen in this pass as a batch.</p>
  </blockquote>
  
  <p>Why is changing a constraint inside <code>updateConstraints</code> actually faster than changing a constraint at other times?</p>