There are advantages and disadvantages to both approaches. With combined sick + vacation, usually called PTO, workers are more likely to try to save PTO for vacation and work when they are sick, and they end up transmitting infections to other workers. Personally, I am a big fan of separate vacation + sick leave.

The counterargument is that some people abuse sick time. (I think there have even been studies that show a large excess of sick days on Monday.) And from a purely utilitarian perspective, why should an employer care if you're in bed with the flu or climbing a mountain somewhere?

That said, I'm not a fan of the combined system. In a lot of other ways, we expect employers to accommodate employees who may have issues of various kinds. Accommodating employees who get sick more often seems a reasonable extension of that. (And I say that as someone who, touch wood, has largely benefited from a combined system over the past decade or so.)

> And from a purely utilitarian perspective, why should an employer care if you're in bed with the flu

Because the alternative to being in bed with the flu is being at work with the flu, and the employer doesn't want to catch the flu? It kinda makes utilitarian sense.

What I meant was that you're not working so you should simply forgo that day of climbing the mountain. It's a day off work in any case.

As I said, I'm not a fan of the combined vacation and sick time in any case (in part for the reason you say). And, yes, people will drag themselves into work because they don't want to lose a vacation day.

If you use up your combined PTO on vacation, you don't have any left when you actually get sick.

If you hoard your PTO in case you get sick, you don't get to enjoy vacations.

There's a middle ground, but the spot where you draw the line and say "I need to save this many days in case I get sick" is going to be different for everyone, and most people are not going to calculate it correctly.

Not to mention the employee isn't incentivized properly here. The employee that takes too much vacation and goes to work sick, they're not the one who pays the cost of them going to work sick, it's the other employees who do. So a combined PTO scheme like this actually incentivizes employees to err on the side of taking more of it as vacation than they should.

People can typically borrow against future PTO if they get sick and don't have time banked. Again, I don't advocate a combined system and I actually agree the incentives are mostly wrong (for everyone except those who abuse sick time when they're tracked separately which are probably less common among readers here than in the general population).

Indeed, approximately 40% of sick days are used to create effectively 3day weekends (Monday or Friday)

I get the joke but I’ve seen references to at least one study that found 35% of sick days were taken on Monday which is more than random chance.

This doesn't seem odd to me. People go out on weekends and are in contact with people they aren't normally around.

People get sick doing stupid stuff in the weekend?