Hard Start:Consists of a Potential Relay and Start Capacitor. The purpose is to overcome high starting torque.
True with age, compressors start to develop characteristics of higher torque from age, and power factor problems the most evident is the so-called "brown-out" conditions from the electrical supply. (Con Edison,LIPA,PSE&G) for example.
PTC relays are now the norm from appliance manufacturers.
Unfortunately, this is the reason for so many problems as there is trace voltage present at the windings, even when the compressor is off.
The "Hard Start Kit" as being sold is a solid state device which incorporates the same principles of relay & capacitor.