The science of ballistics is well researched and mature given its centuries long importance to the defense of every nation. It was for trajectory calculations that computers were first invented.
That said, I expect that pretty much everyone agrees with you about actually testing a new gun, scope or load before using it for hunting; it's just common sense. However, it's impractical to test every load under the wide range of conditions commonly experienced in the field, or to evaluate new loads, bullets, and calibers at the shooting range to find those that best fit a particularly need. That's where ballistics software comes into play.
I use the JBM site when posting numbers because it's free and everyone who's on the internet has access to it, and thus, they can go check my numbers for themselves. For my own exploration of the subject I use installed apps because they are faster, don't rely on a clunky webpage interface, present data in many different ways, include tools not offered on-line, and allow me to simultaneously compare multiple independent shooting scenarios.
I don't buy a gun or come up with a load and then wonder what it's good for. I start with what I need from a gun or load and use ballistic apps to find the best caliber, load and bullet for a given job. Buy, build or load the particulars and then go shoot to fine tune it. I expect lots of other shooters do likewise.
