I am developing a web application which contains a user login. In the web I have seen that many web applications do not allow users to change the username once the account is registered. Is there any reason for that?
I think it's more personal preference to be able to keep track of who posts what rather than any real security concern. I see no security issue in allowing a user to change their username, but you will have users that try to imitate other usernames and admin usernames to confuse and possibly socially engineer information.