When we change a user profile the changes don't affect current sessions instead they take effect only in subsequent sessions. if we need to know if a session uses the before_change profile or the current profile we still need the time of profile modification to compare time of session logon but if we don't know the last information we can't get it.
it's preferable to have this information in some views (like v$session) so it can be easy to know which session is affected by the modification or still running in the old limits.
Thanks.