[Exploring]

I have seen in many papers the measurement of the QUANTUM YIELD. However, I do not see what is the practical use of it. Any suggestion?
thanks

[Babcock_Hall]

Have you looked into photosynthesis at all?

[wildfyr]

It helps us gauge how efficient photoreaction is.

[Enthalpy]

In many cases, the quantum yield is the hard limit, hence it tells you, better than a power yield for instance, how far a process is from the best possible yield. This makes it also a tool for understanding.

Take for instance visible light on a silicon photodetector. You get almost on electron photocurrent per incident photon, which is the limit. It explains you why amps of photocurrent per watt of light drop at shorter wavelength: just because a joule of blue light contains fewer photons than with green light. Having checked the quantum yield, you know that competitor detectors working similarly won't do better.

[Exploring]

thanks a lot for the answers, especially to Enthalpy.
I  know what is about. 
However, in real industrial examples, I was not sure how important is that measurement, and how to compare among samples.