What is the difference between the User scope and Application scope in app.config?
User-scope settings are used to store values specific to each individual user, whereas application-scope settings are used for all users.
Take a look at this article.
User Scoped Settings will only affect the current user and are relatively safe to set. They are stored in a user specific location so there is no real issue with writing to them.
Application Scoped Settings on the other hand are read-only and cannot be changed