I logged in only to join this chorus.
I do curriculum development on Macs, in the always far, far superior Windows version of Microsoft Word.
I pirated my first version of Parallels 3 from TPB, and then bought Parallels 4 when it first came out for stability and updates and because it was such an improvement over version 3. I have bought every upgrade through version 12.
Once upon a time having a license key meant you could install Parallels on up to 5 computers, then it was 3, and now it's 1 with Parallels 13. I've worked with the dwindling license versus installs situation by not upgrading some computers or not upgrading the versions of Parallels running on them. At this moment, I have Parallels 12 on three Macs, Parallels 11 on another, and Parallels 10 running on a laptop I hardly ever need.
I won't be purchasing version 13 at the price offered just to use the software on only one of my production machines. How could I even choose which machine? The one at work where I push final documents, worksheets, and textbooks? The one in the company housing where I tinker during the week? Or the one at home where I often work through a weekend right up to a deadline?
The simple answer is to avoid this and not choose to buy Parallels 13. If I need new software on more than one computer, then I will buy from your competitor or take my family out to dinner instead because buying a single use license for software that is needed on more than one computer is a waste of money.
I have been using Microsoft Office 2003 for more than 10 years and last week I purchased an Office 365 subscription because MS Office 2003 is starting to slowdown my workflow. My new Office 365 subscription lets me install what I need to get work done, inside Parallels 12, on all 3 of my production Macs, and any number of phones, tablets, or other devices. It does this for not much more than the cost of a full, single use Parallels license. That's a good deal, and one which convinced me to start moving away from 15 year old software. Parallels versions 5 through 12 still work just fine too, so I expect I'll get around to eating the cost of a new Parallels license in about 2033. See you then.