Bitcode makes crash reporting harder. Here is a quote from HockeyApp (which also true for any other crash reporting solutions):
When uploading an app to the App Store and leaving the "Bitcode" checkbox enabled, Apple will use that Bitcode build and re-compile it on their end before distributing it to devices. This will result in the binary getting a new UUID and there is an option to download a corresponding dSYM through Xcode.
Note: the answer was edited on Jan 2016 to reflect most recent changes