There are always individuals who will push the boundaries, in my experience.
During my working life, I had a mixture of Freelancing and employment. As has already said, as a freelance, no work means no pay, so, there is an incentive to drag yourself in, or, in my case as an IT Contractor, work from your sick bed.
I did have a prolonged (for me) period of sickness, after a heart attack (two months off) fortunately I was in full time employment at the time. The employment included 6 months full pay sick and 6 months half pay.
The most extreme case of "pushing it" I recall, was when I was Contracting at CQC. There was a young woman who was frequently absent for a half day, or few days. Over the time I was there (about 12 months), she often talked about "having to care for Henry". I naively assumed "Henry" was a Parent, Partner or at the very least, a human being, I subsequently learned that "Henry" was a horse.