Motivation
Modern computers are extremely fast. Utilise a little of that power to provide you with very fast feedback as you're doing your work. You don't even have to hit a keyboard shortcut anymore.
Applicability
This is a useful tool if you're somewhat accustomed to test-driven development.
Application
This is a very simple addition to your day to day work as a software developer. When performed in a TDD cycle, you know exactly when you've written enough code, because then the test will turn green.
Consequences
As a side effect of running your tests this often, you might become aware of the actual time your tests take to run. Are all tests as still as valuable as when you wrote them?
Samples
Infinitest for Eclipse and IntelliJ.