Have you ever heard of the Puppy Dog Close?
Imagine you're the owner of a pet shop and you want to sell a litter of puppies. If you just let people come into the shop and look at the puppies, they may bond with them or they may not. It's all a bit hit and miss. So instead you let them take the puppy home for a week. When you call them a week later to arrange to take the dog back, 90% of people refuse to let it go. They're sold.
Giving some kind of free experience to people (whether of your time or a product) is a variation on the Puppy Dog Close.
I'm not a big fan of giving away your time. There are a lot of risks that go with it, which I discuss with my clients and workshop attendees, but as long as you're aware of the dangers, and learn to manage them properly, it can be a good way to build your business until you've mastered the art of marketing.