I don’t know how the idea of the “One Month Free” software started – whether it has to do with purchase order cycle, or moon cycle.

From the end-user perspective, if the software is a “One-Off” application, one month trial is far too long. The user will  use the application and forget about you and your software. You should offer a shorter trial period, instead. On the other hand, if the software is a long term application, there’s no reason to limit the trial to 30 days. It would be better to implement functional restrictions. Even with limited features, the software will remain on your customer’s desktop, used from time to time.

I think the “one month free license” does not increase software sales, although many companies offer it.