title: Please explain the purpose of Always Embed Swift Standard Libraries
body: <p>I thought I understood what <code>Always Embed Swift Standard Libraries</code> was doing, but now i'm confused.</p>
  <p>I pushed an update to a <code>MacOS</code> app to the App Store and a user said it was crashing for him on <code>macOS High Sierra</code>. After a very quick investigation, it seems the swift libraries were missing and one of my frameworks was written in swift (Main app was <code>ObjC</code>). I switched <code>Always Embed Swift Standard Libraries</code> to <code>YES</code>, re-uploaded a new build and everything was great with the world.</p>
  <p>I have now uploaded a brand new <code>iOS</code> app to <code>Testflight</code> that is build for <code>iOS 9.3+</code> and remembered about this issue so thought i'd test it out.
  The <code>Always Embed Swift Standard Libraries</code> setting is set to <code>NO</code> which must have been the <code>Xcode</code> default. I downloaded the app through <code>TestFlight</code> on an <code>iOS 9.3.2</code> device expecting it to crash on launch, but no, the app works perfectly fine.</p>
  <p>How can a <code>macOS</code> app crash running on 1 major version behind of <code>macOS</code> but an <code>iOS</code> app can run perfectly fine on <code>iOS</code> that's 4 major versions behind?</p>
  <p>Am I completely misunderstanding what this setting does?</p>
  <p>When should we use <code>Always Embed Swift Standard Libraries</code>?</p>
  <p>----- EDIT
  I've just checked the <code>.app</code> contents and it seems it does have the swift libraries in it, which would explain why t didn't crash on <code>iOS 9.3.2</code>. So an additional question. Why would the swift libraries be there when <code>Always Embed Swift Standard Libraries</code> is set to <code>NO</code>?</p>