Say that Brother Johny and Sister Sally get a little too 'juiced' up on their Swigg soda's and end up getting a little funky.. or, Elder Anderson has a weak moment at a party and tries some Aunt Jane.
95% of the time they feel guilty and self-report to their Bishop. The Bishop has them go through the repentance process and the issue is closed. The HC doesn't even get involved.
When things continue to happen over and over (Johny and Sally are expecting baby Gideon.. or Ender Anderson is putting up rasta flags and his GPA has gone up in smoke)... that's when the HC office gets involved.