Hello b1izzard,
This is generally used to ease the amount of clicking (and for consistency) when deploying/expanding large clusters, or deploying a large number of clusters (e.g. 10-100) of a homogeneous, static and green-field nature - e.g. ones that don't have existing configurations (including networking for iSCSI/FC storage and/or FT-logging) and are not intended to have their networks changed from what is decided at the start.
However this is at the expense of potentially annoying alerts/warnings if manual changes to the networking are made later, as then the hosts would not be compliant with the Quickstart configuration, my understanding is that editing Quickstart configurations and/or forcing compliance after the fact (and hosts have been deployed with it) is still not an option in 7.0 GA (but I will validate this as it has been a while since I checked for updates to this feature).
Not to speak badly of Quickstart (but admittedly it clearly does need more fleshing out and flexibility), if it was just a single cluster of 3-10 nodes, I myself would likely just manually configure it (and/or use scripts to configure and validate it if feeling lazy/scripty).
Bob