Its a negotiated benefit for when you are sick. The small percentage of pilots who abuse it cause harm to the rest of the pilot group. It results in concepts like verification and changes how trips are awarded and who gets them. A obvious example is the what some call tactical sick leave to increase their GS awards. Abuse can also cause dramatic reductions in the benefit when the company has negotiating power as we saw in the chapter 11 contract.
Using sick leave is really simple. If your sick don’t come to work. If you are well show up.