Which version of Norton Internet Security to install?

I am wanting to install NIS onto a second PC but do not know which download to install as there is a pretty big difference in size :

 

NIS-18-1-0-37-EN (91.2 MB)

or

NIS-NoDefs-18-1-0-37-EN (39.3 MB)

 

I presumed that the NoDefs didn't contain any definitions and would be downloaded and installed on liveupdate thereby taking a lot longer to complete liveupdate, but liveupdate seems to download and install similar updates in a similar amount of time with both installations.

 

So which one should be installed onto a second PC ?? it seems a waste of time installing the bigger download if the smaller one works and liveupdate doesn't take any longer ??