For a lot of users Prizmo can see like a real niche tool, however i have found it useful in some of the most bizarre aways in my regular workflow. When i look to buy any software--like any other tool--i look at the perceived ROI. I have to admit that Prizmo didn't seem like it had much at first. However i had first gotten a copy as part of some other flash-sale like deal in the past, and started using it for 1 feature alone and have found it useful in a handful of small, strange ways since.
My first real use for this too was as a fast way to unskew whiteboard pictures--i am a mobile application developer, and since cellular cameras have gotten so good, we rarely copy them down in notes anymore--I had an iPhone App for this, many actually, but found them to be reasonably rough to use on such a small screen. Now i just send them to myself as i take them, use Prizmo to straiten up on my Mac and save them to Evernote.
The completely unexpected use i found was the handiness of having a live on-screen OCR tool. What i mean by that is Prizmo can sit in your menu bar--not a new feature so many apps do it, i now have too to simply manage that--however, one thing i do find really cool is you can tell it to OCR the screen, it will give you a cross hair cursor and you can lasso a portion of your screen, it will then OCR that section and copy it to your clipboard for further processing. I use this to copy content from things like the Mac AppStore, UI elements that I'm putting in documentation and would like the exact text too, extracting text out of protected PDFs for simple things such as extracting times and costs rather than retyping it all--did this for my mortgage, put it through Soulver and saved me and full of pricing questions--its an incredible feature, and since i use many Virtual Machines for my job (Linux, Windows) and Simulators and Emulators for devices (Android and iOS) this feature transitions really well to any of those programs to simply grab the text on the screen.
Anyway i know some of these are narrow uses, but i felt the need to simply point them out as for me it is an oddly unique part of my personal workflow.