Management at my job keeps such a skeleton team that if someone can't make it for some reason , it's a headache . A scaramble. People would be asked to come in on their day off and/or overexert themselves . 
I'm sure you're thinking that it's because of the cost of getting new people . No. They have the money . They always brag about how much profit they're making . 
I for one am not working harder for such an easily avoidable problem.