I'll bite, well nibble.
@brandon429 has a laser focus on fish and other livestock health.
In this he is 100% accurate that Nitrite is a non factor for the health and safety of livestock in a reef tank.
Let me make the case for why a nitrite test is worth doing, or at least worth having.
1) To let you know when you can start testing for NO3: When there is NO2, an NO3 test is almost meaningless.
2) To demonstrate actual classical nitrification: a ton of things eat ammonia - algae, coral, anything photosynthetic, heterotroph bacteria if they have a carbon source ( which algae also provide). So Ammonia will go down in any system with the lights on. If that's all you care about, then fine - your fish and coral will be happy. But if you actually want to see if your system is doing bona fide nitrification, then you need to see ammonia go down, and NO2 be produced.
3) some systems manage to keep a persistent low, but well quantifiable level of NO2. Lasse and Dan_P have found this to be the case in their systems. If you are wanting to fine tune your NO3 to keep say 1-2ppm, then correcting for a tenth or so NO2 can dial this in properly.
To repeat: None of these things have a bit to do with keeping fish and coral alive. If that's the extent your concern - and for any brand new hobbyist, it is - then NO2 can be ignored except to say NO3 tests will be garbage for a while.
Regarding point 2), Brandon, just imagine me being the constant devil on your shoulder that every time you declare a tank is cycled, I say - "actually he just means it eats ammonia. To show traditional cycling is established requires seeing ammonia go down and NO2 go up. Without that, you just know something ate ammonia, and a lot of things eat ammonia."
( I wouldn't actually do that, it would be exhausting for everyone. So you'll just have to use your imagination

)