The reasons for working in the same room are many, but there's also some trade-offs. First let's look at some indications of proximity (working in the same space or co-located) on communication (and therefore on productivity - my assumption).
There’s some work done on "proximity" and it’s impact on communication and knowledge sharing.
Link to a Google paper.
This is related to "how people behave, and how that is affected by proximity". It is only laterally about "knowledge sharing in a office environment", but does point out that if you want people to behave "consistently" you need to put them close together(see table 13, the correlation on behaviour and proximity).
Book by Alistair Cockburn that mentions cost of communication (and Osmotic Communication)
In the first edition of this book chapter 3 is entirely about communication, it’s cost and the impact of office layout on communication.
Again no hard figures on productivity, but since we transform “knowledge/information” into customer value, it is hard to make the case that an office layout that makes communication harder can be good for business.
There are some caveats to this. For example you need to consider the need for “silent hours”. Hours in which no-one is allowed to interrupt the rest of the room (if you have a team room for example).
The company where I'm currently working has opted for a mixed layout. We have team rooms, but we don’t have a full open space where all teams would be located. That is seen as balancing the problems with interruptions with the need for communication.
How did you solve the trade-off between communication and avoiding too much interruptions?