You can install prism on 2 computers.But you can enable and disable license on computers so that you can install the software later on for instance on a new computer.
I copied a comment from Hamza :
"I understand your concerns so let me clarify. The 2 licenses are to satisfy the common requirement for a less powerful more efficient PC for capture in the field and a more power hungry one for processing.
De-activation of licenses: there is a built in tool that allows you to see how many license instances are active on the server but more importantly, allows you de-activate and register your keys at will.
We understand the need to move license for one reason or another and PCs are not impervious to breakdowns."