When you have more pedals on your pedalboard than your power block can handle, then you need something like this. Just be sure to check, first of all, that the total need of mA from both pedals doesn't exceed the mA output of the power block's port you'll use, and secondary, because the aforementioned pedals will not be isolated from each other, that there is no mains hum from them. So, how many pedals on our pedalboard are too many?