>A buzz a couple days ago will not fail a test.

I don't think that's true.

  Your first use will usually stay in your system for 5-8 days
  If you use cannabis 2-4 times per week and then stop, you’ll test positive for 11-18 days
  If you smoke 5-6 times per week, it’ll stay in your urine for 33-48 days
  For Medical cannabis patients and people in the #smokeweedeveryday club, 
  THC-COOH will stay in your urine for 49-63 days

https://herb.co/2017/02/09/heres-long-weed-stays-urine/

Even if it was true, the fact that it is so easily passible doesn't help the argument that it's not pointless and arbitrary.