In recent years I have seen a number of companies switch from having separate vacation, sick, and personal time off to an integrated PTO system. Regardless of the reason for not attending work, the employee is charged against his or her accumulated PTO accrual.
While there may actually be a reduction on the aggregate days allowed as PTO, the main motivator appears to be to reward the healthy or conscientious employees who never take a sick or personal day, and provide a deterrent to those that habitually manage to use every single hour of sick time accrued.
Now I have come across a company wanting to change back from PTO to separate plans for vacations and sick days. Their reason is that employees were so motivated to avoid sick and personal absence, because they could add to their vacations accrual, that the Company saw a significant increase in its accrual overhang. While vacations are a legal carry forward entitlement, sick days were use it or lose it and there was no carry forward entitlement.
I would be interested in hearing any views and comments from those with experience of the change to PTO (or back) and what evidence there is to suggest that sick day entitlements are commonly abused.