The background signal keeps your Bluetooth device always receiving audio, so it never cuts off the attack of each click. Raise it slowly until the click stops sounding chopped; start between 5 and 15%.
During silent bars the background signal keeps going, so the first beat isn't lost when the click comes back.
Many Bluetooth devices, like the Fender Mustang Micro and most wireless headphones, stop passing audio when there's silence. A metronome is exactly that: a short hit, then silence. When the next click arrives the link takes a few milliseconds to wake up, and you lose the attack.
Bluetooth Metronome plays a very quiet background signal between clicks, so the audio never drops. It also has drum grooves, tap tempo and silent bars to train your timing.