The problem obviously comes when you need a new computer pre-loaded with Yosemite or later, or you need other software that won't run on the older OS. From my point of view the annual updates of OSX is getting to be a bit of a pain. One reason I bought a new 2012 Mac Pro tower before they disappeared. Have 3 boot drives in it and will be adding a Yosemite drive or partition soon for some other software that needs it. Whether it will work with OS's after Yosemite is open to question. Also have a Late 2013 new Mac Pro that I am keeping on Mavericks until I have to move, or add a partition or two for dual or triple boot to the 1TB SSD. Definitely a hassle.
Sony PMW-EX1, Pana AJ-D810 DVCPro, DVX-100, Nikon D7000, Final Cut Pro X 10.1.1, Final Cut Studio 2 and 3, Media 100 Suite 2.1.5, Premiere Pro CS 5.5 and 6.0, AJA ioHD, AJA Kona LHi, Blackmagic Ultrastudio 4K, Blackmagic Teranex, Avid MC, 2013 Mac Pro Hexacore, 1 TB SSD, 64GB RAM, 2-D500: 2012 Hexacore MacPro 3.33 Ghz 24Gb RAM GTX-285 120GB SSD, Macbook Pro 17" 2011 2.2 Ghz Quadcore i7 16GB RAM 250GB SSD
Jim, you're so right. It's all the 'updates' that case so much confusion. As with most of the situations in the world, it would be nice to say, "right, let's pause here for a few years while we all catch up". No chance I'm afraid, man wants to 'progress' come what may.