I made a little change in the file ionic.bundle.js.
Unexpectedly the change work on an android real device.
My question is, when is the ionic.bundle.min.js file used by the framework ?
Thanks 
When you create an ionic app from the command line i.e. ionic start myApp it provides you with all of the Ionic files you can use, but you don’t have to use all of them. If you look in the index.html that is added you’ll see it is including the ionic.bundle.js file and not the ionic.bundle.min.js file.
Some people change the index.html to include the minified (ionic.bundle.min.js) file instead of the normal (ionic.bundle.js) file when releasing to the app store in order to improve performance. But, if you ever need to debug something caused by the Ionic code, the normal (non-minified) file is easier to sift through. So, to answer your question, the framework will never use it unless you tell it to.
Also, I wouldn’t recommend making permanent changes to this file, since this will be updated in future releases and you will lose any changes made.