When I recommend software tools, I have a few favorites, including Cleanshot X, a fantastic screenshot tool that has enhanced my ability to communicate. Recommending paid products like this, given a wide enough audience, never fails to solicit a certain type of comment:
I respectfully disagree! And I'd like to make a case that a different perspective can put you in a different league of software engineers.
Expensive is a loaded term. I don't know your financial situation, but I think two things are true for the professional or aspiring software engineer:
On to the second part of the sentence: "...for something I can do for free." Having used both Cleanshot and Mac's equivalent tools, I can say with confidence that this is inaccurate. You can't do the same things, and when you can, it's harder.
We aren't even digging that deep. Paying for tools means you get these features. And, because the creator is getting paid, they keep adding more! Is Mac adding features to their screenshot tool? Not at nearly the same rate.