(Same question about covid/flu tests - a lot of people act like taking a test is part of a treatment regimen, but it kinda isn't. But those are still useful since you might be an asymptomatic spreader.)
When you're trying to understand a complex system, it's best to start with things you can actually see directly. Doubly so, if you're going to try and change something.
Coding analogy: there's a reason "Hello World" is about printing stuff to console, and the very first thing you do when writing to a new target, or reconfiguring some application, or testing unfamiliar commands, etc. is something where observable output directly reflects the changes to inputs you make. Otherwise, you don't know whether you're doing things right, or doing anything in the first place.
WRT. COVID/flu tests. You or your kid come to the doctor with a running nose and some cough. The test is useful to tell you whether you're dealing with one of the "heavy hitters" like the flu or COVID or RSV, or just a bog standard ${random kindergarten viral infection} that's treated by nose cleaning + anti-cough medicine + pretending you're not sick anymore, or whether this stuff is bacterial and maybe you need another swab to pick the right antibiotics.
Some color patterns in cats carry healthy problems. Breeding for white cats with blue eyes for example is discouraged, because they born deaf.
It may start in any BRICS country, and then expand! Tourist trips to cat cloning resorts. Check our CATLOG!
https://en.wikipedia.org/wiki/The_Windup_Girl
(Cheshires are a thing in that book, bio-engineered cats that can change fur colour like a chameleon/octopus/squid to exactly match their surroundings. They breed and devastate the world's population of small animals such that there's a bounty for every one killed. I'm trying to remember where I read a great critique of the book, especially the cheshires, but I'm not finding it)
Edited to add: found it: https://www.nyrsf.com/2015/10/eric-schaller-the-problem-with...
First line treatment for covid/cold/flu is fluids, rest, and at least a bit of isolation.
But if you need more than that, it's useful to test for what you might have, as further treatments vary.