"Was that in the notes?"
"Where'd you learn that?"
"How do you just know that?"
These are all questions I've been asked, in one form or another, over the last 10 years of working in IT. The situations vary, but there's a common thread to each - an issue identified, a problem solved, a better way to complete some task.
Most of the time, I don't answer. How do you explain that you knew that one specific thing because of the three hours you spent last month sitting in your cold basement, begging your production NAS to start back up after an upgrade? Well, it's not production, per se... but to your family or roommates, it may as well be. "It's a long story. I've seen it before. Not here - on my server at home."
Engineering knowledge is a perishable resource. Its decay comes not just from continual technological advancement, but from your own experiential half-life as well. I haven't touched a Cisco device in over a year and my last Cisco cert has since lapsed. I could still poke around in the IOS CLI with a little fumbling and an embarrassing overuse of the
?, but I doubt I could set up an eBGP neighbor on-demand without a reference page and a few minutes of review to jog my memory.
Other times, it's not even the knowledge itself that you benefit from. The information is out there - you're free to access it as needed. The concepts are what you really need to succeed. You'll have a much harder time accomplishing things with the reference pages and a few minutes of study when you never had the opportunity to explore routing and BGP concepts in the first place.
Having a homelab is a quick and easy way to stand out as a professional. That statement holds true whether you're a specialist or a generalist, a 10-year veteran or just starting out in Tech.