Even more problematically, if you have a free service that could attract any kind of automation (e.g. an API SaaS with a free trial) then you're also going to get a lot of "users" who seem to be the "truck drivers" given a black-box usage profile, but who will also never actually convert. They use some free part of your service a lot, but they're not and never will be interested in any paid part of your service.

Maybe a close analogy would be: truck drivers who stop at your rest stop every time they come by... just to use the washroom. But who never go into the store itself.