There are very significant advantages to using Linux on the desktop in some cases.
Take for example what used to be called Windows Terminal Server (which still exists though the name keeps changing.) This works not too badly, but the cost is massive. The Windows licensing costs for just five users can be as much as for the server it's running on, and that's before you start considering application licences; if you want to add more users, you have to keep buying more licences and managing them is a complete pain the neck no matter what anyone says.
With Linux, this stuff is (certainly used to be) second nature, and you can keep adding users until performance starts to suffer - no extra costs, the money you save on licences could easily pay for another server or two and you don't have the worry of managing the licences either.
The technology to do this has been in place for ever and works very well (for users on the other end of a WAN, something like (Free)NX solves performance problems) - what's really missing IMHO are tools to easily set this up and then configure and manage (i.e. change, lock down, remotely take control of) the desktops users see.