Surge protectors usually are triggered and reset when there is a potentially damaging electrical surge in signal cables. Only when the surge goes above 20kA or more do these devices fail, which is what can be seen in the photos below.
When these types of surges occur, without protection, the entire panel would likely be destroyed. Instead, a small economical device takes the hit, breaks the circuit and the entire panel is protected.
The photo shows a melted and exploded-looking MTL SD32MDX. The energy this device was able to take and divert saved the connected sensitive electrical equipment from destruction.
For around $100 a piece you can potentially save thousands in repairs and replacements with a simple installation of a surge protection unit.