Most of my past projects are bad at collecting money. Some are literally incapable of it. Of all the mistakes i've made as an engineer, i list this among the worst.
Gone are the days when e-commerce was a complicated and concerning development. Now, websites with basic integrations can securely and flexibly offer purchase options to their customers. So, if implementing purchase options is easy, and the benefits include getting paid, why haven't buy buttons become project staples? Why aren't buy buttons as routine as user logins?
Rule of thumb: if your project is robust enough to merit logins, it should also be able to collect money.
Money brings a number of benefits apart from just being money. Many are psychological. The first time you receive a payment for your tool, you will be introduced you to an addicting feeling. Not a feeling of greed, but one of pride and justification.
The notion that someone is paying for your tool is the greatest indicator that it's providing users real value. The first payment seems to instantly validate the days/weeks/months you spent building something. In my experience there is no faster way to get excited about working on a side project than to know people are using, and paying, for it.
The saying goes, "time is money". But in the case of side projects, time can only become money if we give users a button that enables it.
So the next project i build is starting with a buy button. Because the worse case scenario is no one clicks it. But the best case? Well, that is the exciting part.