When we first started Doodlekit we had a limited 30-day trial membership. We thought it would be enough of a taste to get people to buy our product. Unfortunately it wasn't a great success. After thinking about it for a while, Heath and I decided to make a plan that was completely free forever. The results were instantaneous. We started seeing signups like never before and our profits climbed like crazy once we introduced Doodlekit as a FREE website builder.
Before I go any further let me clarify that this only works if you actually have something else to charge for. The "give everything away for free and figure out how to make money later" model is broken and unsustainable. Free is a segue into the paid products and services.
So why didn't the trial work? A free "Trial" is not free enough. It's still too binding. People have already been burned by magazine trials that start charging automatically, or shareware that stops working before you get a feel for it. If there are really no strings attached, the customer is much more likely to stick their toes in the pool.
One of the most effective marketing tools is Word-of-Mouth. The paradox of course is, "how do i get customers talking about me if I have no customers?" A large base of free users isn't terribly hard to build up, and if you can impress them they'll be sure to tell their friends and colleages.
Assuming you ask for an email in exchange for the free product or service, this gives you a great list for marketing. The best part about this list is that you know the customers are interested in what you have to say, they've given you permission to tell them more about the product. This is worth much more than Google Ads or blind Bulk Mailers. You've already engaged the potential customer in a conversation that can lead to more business.
The only trick is finding that balance of what you can afford to give away. For us, the cost of hosting all the free sites is trivial compared to the return. Much less than hiring an Advertising Agency.
By giving our product away, we've been able to keep our business profitable and growing. You could too.