Having the chance to work on your programming files can be a great thing, the issue you may face is not knowing about how you can save the files properly with the local settings. Once you know about the PBXUSER - Xcode Project User Data File you will be able to do this, but also have your computer working properly for all of your needs which you may have. Without this, you can have trouble in getting to enjoy the programs which are present.
The main reason you should be using the PBXUSER - Xcode Project User Data File is it allows you to have the files saved properly on your computer and be able to open it later on. When you have the chance to open the files later on you can easily start your work right from where you left off and not have to be concerned about it not being done to the proper level because of what you had to stop to go do.