I will give you my example here. I don't want to out myself so will try to be generic, you'll get the story. My group tests software 'widgets' - there was about 10 of us doing this testing and we typically put in about 50 hours per week, each of us.
We've laid off three resources recently, but the volume of work did not go down.
Doing simple math, I can add 30% to my pre-layoff workload, you'd end up with 65 hours per week, that's more than 9 days per day every day of the week including weekends.
That's not sustainable! You can do this death march for a week, two, or two months but after some time fatigue will kick in and folks will either get ill or will leave the company.
Now keep in mind, it takes about a year before a tester is fully valuable to the team, so if we start to lose people we will just go deeper and deeper in the hole.
So, something has to give - and that will be quality of work.
Or software 'widgets' will be less reliable, there will be a lot of unhappy customers, teams, etc...
I hope this makes sense...