I worked for a software company for many years. We had a report-writing tool that was easy to use and we delivered all the pieces needed to use it with our software applications. People could also use it to work with their own (i.e. not sold by us) applications, but to do that they had to pay us for "extended use." The license for using the software to define their own applications was expensive, and clients weren’t buying it, and many of them were using it for their own applications anyway.
Finally, one of my coworkers suggested that we just allow the customers to use it without an extra license, reasoning that the clients would then pay us for training and other professional services to use it. It made all the sense in the world, which is of course why we didn’t do it. "What, just give extended use away for free? No way!"
Of course, there was nothing "free" about it: they paid license fees to us for the applications they bought, the reporting tool was part of the license, it was paid for no matter how you look at it.
In the Old West, taverns would offer a "free lunch" to get people to come in and hopefully buy beer and liquor to enjoy with that free food. Conceivably, a person could go in, avail themselves of the free food, and walk out without buying anything, so there were men who would see to it that the diners purchased something to drink. That was when people learned "there ain’t no such thing as a free lunch," abbreviated TANSTAAFL (now you know what the title means).
Willow had an intereesting take on the subject: she got a plant as a gift from her son, after which he asked if he could use her dryer. I’m sure she would have let him use her dryer regardless, but he felt it was necessary to offer something in return. She called it "Family Communications."
And I don’t think I need to say anything about a "free puppy" or a "free kitten."