when you don't provide credentials it tries to login with OS User available in Teamcenter,
if it is asking for credentials it means that user is not available/inactive in Teamcenter.
anyways if you don't provide credentials you will not be able to perform any administrative thing,
So its better to provide credentials (also better practice to use encrypted files for command line logins)
Thanks Ganesh for the clarity!!!
I have tested the scenario by adding my user id in teamcenter organization . now it is started working without asking credential. Also noticed that it should be added under dba group.