There were (are?) two types of socket "buttons". One type uses a diode; the other a thermistor. The diode type cuts the power to the lamp by 1/2 which translates to a light output reduction of 2/3. Lamp life is long to indefinite. The lamp also flickers more and that bothers some people.
The thermistor button starts the lamp at a low voltage when the switch is turned on. Then it ramps the voltage up relatively slowly which some say lengthens lamp life. But there's also a few volts drop across the button so the lamp doesn't see the full socket voltage and that lengthens lamp life too. A problem, however, is the thermistor itself. It's a resistor and so generates heat in the socket. Sockets are designed for heat from the lamp; but may not be able to handle the extra heat from the resistor.
TKM