Open plans promote collaboration.  However it is critical to have the right mix of open and private spaces.  Some employees cannot function in open spaces.  Some need to be on the phone or in conferences.  Even those who can work well in an open plan will still need a private space for conferences.  Some open plans may not be providing the right mix of public/ private spaces.   Our experience would show that there be at least one private space per 1000 square feet, and this ratio should be increased for a density above 5 employees per 1000 square feet.

Who Moved My Cube? – HBR.