Actually there are two ways you can handle mounting:
1) You install the supermounter (submount) and you do not have to take care about mounting
removable media (floppy, CD/DVD, Memory Cards, etc) at all. This is done automatically
2) The "traditional" way, where you need to mount the DVD *every time* you insert
a DVD/CD in your drive *and* unmount when you would like to eject them.
One exception are Audio-CDs which you can not mount.
Which option you will use depends on your preferences.
Although I think that submount is a nice thing, I prefer the
traditional way, since I have always done it that way :-)))
The noauto option tells Linux not to mount a Filesystem (in this case the DVD)
at boot. The reason why I use this option is because I have configurde my DVD as alternative boot device.
So when booting my Linux from hard drive there isn't any media (CD/DVD)
in the drive, therefore an attempt to mount the DVD during boot will result in an error.