20k will be roughly 6 months take home pay for a lot of people, which is the recommended amount to have in cash as an emergency fund.
It depends on where you are in life though. After buying my first house I was left with about 3k in savings, which is probably the lowest it’s been in my adult life, and definitely didn’t feel comfortable.
IMO the importance of cash savings varies according to a number of factors. For example, how long you’ve been in your job and how much redundancy pay you would get if you lost it, whether or not you own a property and have potential maintenance costs, how much you have in your mortgage overpayment reserve etc. There’s more to feeling financially secure than just cash savings.