I was using it but then read that caffeine can inhibit germination so I must admit I stopped adding it to my heap. But maybe others will know more about this.
When you make your coffee most, if not all, of the caffeine will end up in your coffee. Only a very small amount will remain in the ground coffee beans.
Even if some caffeine makes it into the heap I would expect some of that to get consumed by the microorganisms in the heap leaving even less.
Inhibiting germination is only a problem if you plan to plant seeds. If you transplant things stopping the weeds germinating is a benefit.