Holy freak out from a lot of people.
First, Microsoft would NEVER force a completely new UI down our throats without having a VERY simple way of changing it. Microsoft is obviously trying to be innovative and redefine the typical OS. Problem is, some people are not interested in it whatsoever, and for many of us, yes, It would be very counter-productive.
That being said, THEY'RE DOING THIS BECAUSE THEY WANT AN OS THAT PLAYS NICE BETWEEN ALL DEVICES WITH WINDOWS (Phones, tabs, computers etc..)
This isn't mandatory, just an option. For some devices, you'll want this. For desktop, obviously not. However, some people are incredibly dumb and may prefer this tile setup for their desktop; at least give the window lickers the choice.