Free trials might even be as beneficial to developers as in-app purchases, which are generally the most lucrative app monetization scheme. They would both employ the same strategy: encouraging a large number of downloads and then monetizing some fraction of those.
I don’t know about you, but a common interaction I have with friends and family members when talking about apps goes something like this:
Them: “So, Shawn, what are some cool new apps?”
Me: “Well I’ve been using such-and-such app lately and it’s really cool. Let me show you.”
Them: “That’s pretty rad. Is it free?”
Me: “No. It’s a buck.”
Them: “Oh… So what other apps have you been using.”
While I do believe having free trials in the iOS and Mac app stores would be beneficial for developers, because it would likely increase revenue as Grossman states above, I also see it as being beneficial for users. People are avoiding a really great app that costs $4 because they don’t want to risk that money on the chance the app is lame (or who knows why they’re not buying it). But it’s an app that could really bring some benefit to their every day life. And so, by allowing a free trial period, that risk is all but removed and a lot of people just might start using so many of the App Store’s best world class apps.