When selecting contactors, you will use one of two common standards: IEC or NEMA. Both match a contactor with the job it has to do, but they do so in different ways.
Using IEC standards, however, you can size contactors very close to their ultimate capacities. In many case, this precision allows you to predict how long they will last. For example, an IEC-rated contactor may run a motor that draws 40A at full load. In that duty, it should last for more than 2 million operation
But, if you use it to consistent jogging and plugging, you would have to replace it after just a few thousand operations.