The importance of sick leave isn't the gross expected balance of pay and work -- as the grandparent points out, for some values those things will be equal, and employees won't prefer one or the other. (Or, better yet, employees might prefer the higher wages because there's more optionality to it -- they get paid more if they're healthy, and they get paid the same if they're unhealthy.)
That misses the point, though. The real importance of sick-leave is about marginal incentives. If an employee is sick, they don't need to weigh one more day of pay against the risk of infecting their coworkers -- they have no incentive to come into the office.
The importance of sick leave isn't the gross expected balance of pay and work -- as the grandparent points out, for some values those things will be equal, and employees won't prefer one or the other. (Or, better yet, employees might prefer the higher wages because there's more optionality to it -- they get paid more if they're healthy, and they get paid the same if they're unhealthy.)
That misses the point, though. The real importance of sick-leave is about marginal incentives. If an employee is sick, they don't need to weigh one more day of pay against the risk of infecting their coworkers -- they have no incentive to come into the office.