Most organizations can benefit from virtualization but the key to understand what problems you are solving with Virtualization, not just blindly implementing them. For example, if you have a fully burdened physical server, it may not be a good candidate for virtualization. For desktops, depending on applications, desktop virtualization may not be the answer. For example. if your primary problem is application compatibility and interaction, App-V may be the better solution.
Systems which are not fully utilized are usually good candidates for virtualization. Other systems which are good candidates are systems which only need to work for a small part of the day.
You shuld virtualize servers that do not habe high utilization…high utikzed servers are not very good for virtualization