Imagine you've left your job, you probably don't want to go back there. You have to start a new job search. You're likely out more than one month's salary. Plus the intangibles of a job search while unemployed vs. employed.
Imagine you declined COBRA, or even with COBRA, you might end up with a period of being responsible for your own health insurance payments, too.
You have a gap in your employment record where you otherwise wouldn't have had one. That affects credit decisions.