No Multisession does not equal 'Finalizing' a CD/DVD.
If you do not finalize a CD, it does not affect the ability of devices to read the disc, such as CD-ROMs,DVD-ROMs, DVD Recorders, etc.
Only when you fail to close a session does it affect playback, as CD-ROM and DVD-ROM drives would not be able to read the disc. And Nero will always close a session, there is not option to leave a session open in Nero.
To close a CD or DVD without adding data, you must choose 'Continue Multiession'.
If you choose 'Start Multisession' or 'No Multisession' Nero will not allow a burn to begin unless you add data. And any data you had already written to the disc would be inaccesable as well, so 9 times out of 10 you would not wish to do this.