Not all operating systems run well on multiple platforms. The main advantage of using just one operating system throughout an organization is increased compatibility and increased uniformity. In practice, the same operating system does not always work the same on different hardware platforms. Often there is a great variance in the quality of the implementation across different hardware and sometimes different feature sets are available. Also, software written for a particular operating system is not always available on every hardware platform that OS runs on.
Some organizations thrive on a mixed operating system environment.
A classic example is that many Windows-only organizations make an exception for content creation machines, which are usually Macintoshes . In a mixed operating system environment, connectivity becomes extremely important. It does not matter if an operating system runs on processors you never intend to use. Please be patient. I am Pentium of Borg, Division is futile, You will be Approximated.