I use this application every day whilst studying. I'm a university student, and I always have tonnes of reading to get through. With this, I just copy and listen to the book I'm reading, rather than directly reading it myself.
Most other text-to-speech apps require that you copy some text, paste it into a text box, and then hit a big "play" button. Clipboard TTS is just automatic. You copy the text, or even an image, and it is almost instantly read aloud to you. So it goes from a 3-step process to a 1-step process.
I usually set my speech speed to 1.5, and I zoom through my required reading in no time!