It really just fragments my knowledge to be honest.
Say "I gotta get things done".
Get me to a terminal. You've got Mac OS command line flags, GNU, BSD. Great.
Then it's some kind of asinine config to interact with some piece of software, all to achieve "generally the same thing", just a different way/flavor.
I really don't see the benefits.
For me, that deeper knowledge is an advantage. It helps me quickly evaluate tradeoffs between databases, debug at the OS level, or dismiss a library still relying on select if I expect heavy load. This insight saves time and increases efficiency.
You've got 2 kinds of cars overall really. Automatic transmission or manual. Get into any of them and everything is the same. Gas pedal, brake pedal, etc.
Objective what you need to get done? Drive from A to B.
It is impossible to drive from A to B with FreeBSD if all you know is Linux commands/syntaxes. That's my whole argument. That it isn't as mild of a jump as driving car A or car B. You are blocked (and need to throw out what you know on Linux for BSD because it'll collide).
Are the differences mild? Sure, but enough to make you ineffective.