The primary reason companies seek to rehire employees is not due to increased production or synergies. In most cases, it is because of two factors: the local service market that employees shop at during their commute and at work, and institutional landlords who are reluctant to accept high vacancy levels and seem unwilling to adapt.
Some individuals in our society seem to believe that we can function solely from a workplace. As well, they often adopt a Theory X approach to management, which is unfortunate. While remote work does not need to be an everyday practice, it also does not need to be entirely absent.
I believe there are some benefits to coaching and mentoring new employees in person, particularly when new systems are involved, as these tend to be better learned through a one-on-one approach. However, most tasks can be accomplished effectively at home. Recent studies have shown that individuals working from home tend to work longer hours and complete more work overall or at least similarly to working in office. (Obviously happier as well.)
However, it is important to note that this is highly job-specific. For example, it is not feasible to build a car from home, but it is certainly possible to write an email or conduct analysis without interruption. My work group is geographically dispersed across the province, and we all function well with remote work. When we are forced to return to the office, we are sitting alone as we were at home, meeting virtually anyway. As a result, less work is accomplished, and there are higher costs for both the employer and the employee.