How will this boost your business' bottom line, and boost it more than alternative investments?
Remember the costs: Not only buying new computers but buying some/many new user applications, retraining users on the OS and applications; rebuilding systems that integrated with the old platform and apps; replacing or rebuilding IT management systems that manage testing, deployment, configuration, patching, and support of thousands (or more) of computers and users; retraining or replacing much of your IT staff; testing and deploying all these things (with newly trained staff using new tools); and all the costly downtime that results from the inevitable bugs of new systems, greatly compounded by deploying all these new systems together: e.g., Why can't they print? The new OS? The new printer driver? The new printer config? The new application? The new user errors?
What does the business gain? Instead of clicking an icon on the Windows desktop, the employees click one on the Mac desktop. Then their application or browser opens and they do the same thing they did last week (except for having to be retrained to do the same task in a new way).
The popular thing to do right now is for businesses to move away from platform locked software completely. So instead of it being a "Windows Vs. Mac Vs. Linux" battle, all internal software is on the web and the desktop only runs Office/browser/email client, etc.
Now, sure, there is some software that cannot be run in a browser. But that list of software shrinks more and more as additional browser functionality is added and libraries make it easier to do complex things.
So the question is: How does this expensive Mac migration pay for itself in the short, medium to long term? And are there other avenues, like web-migration, which could have saved more?
If it's a question of software: IBM is a Linux shop and OSX would seem a questionable plan B after platform agnosticism in the event of a massive retooling due to its BSD lineage and proprietary fiddly bits.
Remember the costs: Not only buying new computers but buying some/many new user applications, retraining users on the OS and applications; rebuilding systems that integrated with the old platform and apps; replacing or rebuilding IT management systems that manage testing, deployment, configuration, patching, and support of thousands (or more) of computers and users; retraining or replacing much of your IT staff; testing and deploying all these things (with newly trained staff using new tools); and all the costly downtime that results from the inevitable bugs of new systems, greatly compounded by deploying all these new systems together: e.g., Why can't they print? The new OS? The new printer driver? The new printer config? The new application? The new user errors?
What does the business gain? Instead of clicking an icon on the Windows desktop, the employees click one on the Mac desktop. Then their application or browser opens and they do the same thing they did last week (except for having to be retrained to do the same task in a new way).