The main point of HS2 is that it will relieve congestion on the existing tracks, and allow more commuter services to run:

https://www.railengineer.uk/2014/01/03/the-capacity-benefits...

http://www.citymetric.com/transport/hs2-isnt-about-north-eng...

The idea that it will turn a load of separate cities into one big city is basically fantasy, as i understand it - this is about HS3, but the analysis is much the same:

http://www.citymetric.com/transport/crossrail-north-really-b...

And yes, i do get all my information from CityMetric, since you ask. It's basically Buzzfeed for transport policy, i love it.