To me there are a few benefits of doing exams (at least the Red Hat ones that are not cheap, but well respected):

1) it looks good on the resume, which can help you get past the initial sift by people who dont understand what your experience actually means.

2) They give you the chance to fill in the gaps in what you think you know. My experience of doing my RHCE after 10 years of professional sysadmining was of the 14 chapters in the book I knew maybe 10 already and had never touched the other 4 because they never came up in my job, and the prospect of a looming exam gave me a deadline and the motivation to actually sit down and learn them, which then paid off later in other jobs that did use them.

3) to test whether you are as good as you think you are :)

If those don't speak to you then they're probably not super important to do, luckily we mostly work in an industry where experience trumps exams.

Which book are you referring to out of interest?

The coursebook I got as part of the training course, this was 5+ years ago so we got a physical book. I've no idea what they do these days but there's a list of exam objectives on the red hat website and that basically covers what you need to know

Is there still an entire section on vsftpd?

no. I don't think that was even a thing in the RHEL7 version I last did and the whole exam/course has changed a lot since then.

I'm sure there are lots of places that still use vsftpd though (I have a vague memory that it supported kerberos at least), so it might still be useful for some people

For your personal development, it offers a structured way to learn a new skill; doing it on your own works, but has the risk of skipping large swathes of it or getting bored with it. Working towards certification is a goal you can work towards, as an alternative to undirected or situational learning.

And for an employer it's a nice tick when assessing candidates, it might just tip the scales in your favors vs someone else. However, I recognize that we're very much in a "seller's market", in that it often feels like education or certifications don't matter when it comes to finding a job, to the point where some years ago, people that just had a crash course / boot camp (as opposed to a formal education, bachelor's or master's degree) could land a six-figure job at a FAANG or startup company.

There was a time (early 2000s) where certifications where all the rage and by far the easiest way for otherwise 'mediocre' employees to stand out from the crowd to get hired and/or a raise. A couple of places I worked had formalized systems tying raises to passing certifications. Several people I know got hired for their job in tech purely on the back of passing their Microsoft developer certification.

I’ve worked at a certain company maintaining Linux servers and POS systems for retail stores across the country. The AD admin was MS certified and apparently among the certification materials they used to recommend companyname.local as the AD TLD. Meanwhile one of our software suppliers pulled samba which pulled avahi.

It became a big headache at first and then we had to adjust all our image build process to avoid the collision between the domain and multicast DNS libraries.

Microsoft certifications back then, yes, practice hard enough I recognised the shape of the question text, and knew what the answer was! Past exams had the same questions as current at that time.