The fruit of thy labours. Inversed: choose your battles wisely if you're inclined to qualify existence.
Put another way: What you get back after putting effort and money into a task.
An important concept here is the total ROI for a task. Often, someone will see a neat toy, recognize some way in which it will help them, but will fail to properly assess its total ROI. A library that gives you some trivial bit of functionality but is extremely expensive and difficult to install and implement isn't worth it. It has a bad return on investment.
ROI in Commercial Software Design
ROI is an important factor when designing commercial software. The customer should get some return on their investment in a product. You could be providing a really neat tool to a user but it needs to have a well rationalized ValueProposition to the customer. It's important to note that a high TotalCostOfOwnership (TCO) could make a ROI proposition moot.