Voltage spikes last only microseconds to milliseconds but can be many times the normal supply voltage. They come from lightning strikes on nearby lines, switching of heavy loads such as motors and welding sets, and grid faults. A surge protector uses components such as metal oxide varistors to clamp the spike and send the excess energy to earth.
Electronic parts are the most vulnerable: digital controllers, inverter compressor drive boards, EC fan motors and LED lighting drivers. A single strong spike can kill a board, and repeated small ones degrade it over time. A surge protector at the distribution board, plus point-of-use protection for high-value units, gives layered protection.
A surge protector is different from a stabiliser: it handles fast spikes, not sustained low or high voltage. It also depends on good earthing, because it needs somewhere to send the surge. In monsoon months, when thunderstorms are frequent, this protection is especially worthwhile.