Publisher is a QV server component that allows for complex Load & Distribute strategies. A QVS SBE-edition has no distribute functions, and only allows for simple reload tasks where you select a schedule from a fixed set of possibilities. Publisher adds all sorts of task types (even jobs outside of QlikView), powerful document reduction and distribution (for example to create a specific document instance for each user with just the data he/she is allowed to see), reloads with a variety of flexible trigger sources, task dependencies etc.
In a default SBE edition, the Publisher is reduced to a very limited set of functions (in SBE it used to be called "Standard Publisher", not anymore it seems) but the complete software is already present. You can buy a separate license that you enter in the Server License->QlikView Publisher screen and TADAA! The fully enabled Publisher is active and extends your QMC with all new functions and tabs.
So you can have it with an SBE, you won't need another installation and it's very easy to activate.