If you set noop on, then services will not automatically op you in rooms you have access in. You can choose to op/voice yourself by using the chanserv op and voice commands.
Example:
/msg nickserv set noop on
This is useful if you wish to enter a room without making it clear that you are an op. If you are an op in a help room, but not currently able to help out, you might want to join without being opped. In general, you will probably want to leave it off for convenience.