Oracle Database Discussions

When we backup the control file to the trace file with the following command:
alter database backup controlfile to trace;
it generates the necessary command to recreate the control file .My question is the currently exists files like datafiles and redolog files will they be deleted and replace with the ones listed in create controlfile command ?
This is one thing ,the other thing is why we recreate the controlfile in noresetlog mode ? don't we need to update the control file with the correct SCN?

Any explanation would be thinkful