I don't know about Sweden but in Finland we get a nice bonus after you come back from your vacation.

This was introduced because in the 1960s and 70s a lot of skilled workforce (several %, tens of thousands of people) emigrated to Sweden, in particular to work for Volvo, Saab and other industries. Workers had their full (4 weeks or so) summer vacation and then left for Sweden, where they were offered a house, a car and a relocation package.

This pattern kept repeating for a few years, so to counter the wave of emigration, the after-vacation bonus was introduced.

I've no idea about Sweden, but one theory could be that you spend more money on holidays. You are eating out, you're spending money on accomodation.

I also do not know why but I've read about encouraging people to take days off has effects like people who are ill taking care of themselves and not spreading a cold around the office and ruining the whole work place attitude.

This is why in sensible countries sick days are not subtracted from your holidays.

Don't know, it is generally mandatory to take 4 weeks, where you can't be denied taking 3 weeks in a row in the months June to August.

I think the idea is that you should be able to spend while on vacation... but not really sure.