I will not send my kids to practice when they are sick, the rule in our family has always been " too sick for school = too sick for after school activities" , it really annoys me when one kid turns up ill and a week later the whole gym is ill.
I've always said school commitments come before gym - so they do miss practice on occasions for school functions, student/teacher meetings etc.
They will occasionally skip a practice for a friend or family birthday - maybe twice a year. A lot of their best friends are in the gym now
Coaches are fine with them missing for all of these reasons. Some kids miss more sessions, some kids less. I guess each family just has to figure out what works for them.