It might help for expensive software but for something that is a few dollars I'd see it as a negative as a developer.
For example with a business app like Grafio, I want to test drive it to see if it works for me. Then I can pay a significant price for the app - if I am using it in a business setting my time is worth hundreds of dollars per hour and the prices of apps are not really a significant expense. I would want development of Grafio to extend further towards supporting my business needs, which is Visio import/export, and I would gladly pay for that feature.
I dislike when the free app is missing important functionality (this defeats the test drive aspect) and I dislike when the in-app is a subscription. I find it obnoxious when apps have too many in-app purchases. It becomes an annoyance to have to pay $1 to read, $1 to write, $1 to save. Just ask $3 for "full functionality" from the start. Don't be silly.
I like when the app is fully functional and I can choose to pay different amounts to support further development.