Who is Snagit For?
If you are a Windows user, and you have only occasional need to grab images of screen content, you may find that Snagit is neither the cheapest nor the simplest tool to use. Anyone who uses a computer may have an occasional need to capture an error dialog to send to someone to get support, or want to grab a recipe from the web, complete with a picture of the finished dish, to send to a friend. Such a person would be well-served by Windows' own Snipping Tool, which is both free and extremely simple to understand and use. And, yes, PrtScn and Alt+PrtScn still work to capture the contents of the entire screen or the selected window, respectively.
If you are a web site developer, a graphics designer, a software documentation professional, or you would like to use captured images in your screencasts or digital videos, a tool with Snagit's rich feature set may be more to your liking.
I do all of these things, and while I find myself frequently going to the documentation or a tutorial to find out how to use something, Snagit does things that I can do with no other tool, like capturing a complete web page, saving it as a PDF file, and have its links still work; or time-delayed captures that allow me to pull down a menu of a program and capture that menu, complete with the highlight and cursor; or organize all my screen captures in a library organized by date, folder, or keyword.
On the other hand, though Snagit, like Camtasia, has the ability to the capture motion on a computer screen dynamically, I wouldn't try to use Snagit alone to do a polished screencast. It's better to spend the money for a tool more suited to that kind of task, such as Camtasia or ScreenFlow, if you need to create and edit that kind of content.