99.99999% of the time, not much will go wrong. Even if the weapon malfunctions, and/or the shooter doesn’t notice the round left in the chamber, and there is a negligent discharge, it probably won’t hit anyone.

Then again, it might. I once watch an (unnamed Arab nation) soldier attempt to fire an M16. Round didn’t go off. He attempted to extract it by pulling the charging handle back, but it was stuck in the chamber. He went through the usual steps of unload, show clear, and out of muscle memory he pulled the trigger as a final step. He had been so focused on doing the steps he didn’t realize that 1) the round was still in there and 2) he had rotated more than 90 degrees and was pointing his weapon at me when he pulled the trigger with a round in the chamber. I don’t have any additional holes in me, so it all worked out. I still think it’s a pretty stupid thing to teach if you don’t teach that you only do it into a clearing barrel or very deliberately pointed down range.