So rather than piss away PTO, I dose up on drugs and drag my ass to the office. If I had dedicated sick leave, I'd just take the day off. But this miserly PTO policy results in me hoarding it.
Usually, the combination results in fewer days of available leave, and since vacations are often planned months in advance, people are forced to come in to the office while sick or spoil their entire vacation by screwing up the itinerary.
It's pretty much inevitable that pooling sick time and vacation time results in a lower total. People aren't really expected to use all their sick time in a given year if ever. But for those who do plan to maximize their use of vacation, it means there's not a lot of margin when they do get sick and it encourages behaviors that aren't good for anyone.
In a few years, the contract will be rebid and I'll roll the dice with my next employer. I rarely get sick, so it's not that big of a deal, but I was highlighting how poor policy can induce sub-optimal choices by the employee.
But a non-trivial number of people have historically abused dedicated sick time; there are even people cheerfully admitting to it on this thread.
Now if I only had 15 days PTO....
Compounding this is the fact that I can only carry over 5 days per year, so at most I can only use 20 days in a calendar year). In a few years my PTO gets a bump to 20 days a year.
Now you must spend your own time recovering from illness that your employer was the primary cause of. That's brilliant right there. U-freakin-S-A.
"Sorry, I'm out of sick days - but as long as I'm here, let's have that lengthy meeting about X. Here, I even brought you a cup of coffee!"