Why? Because a single trace can't tell you if a loss is a bad splice or a bend. By averaging both directions in the viewer, you get the true loss of the event, canceling out the variable of backscatter coefficient. If your viewer can't do this, upgrade immediately. Your OTDR hardware is a $10,000 camera. Your OTDR viewer is the darkroom where you develop the photo.
Don't be the tech who closes a ticket saying "Signal looks noisy." Be the tech who sends a PDF with a red circle around the exact meter mark of the micro-bend. otdr viewer
But the real work begins when you get back to the office. That’s where the becomes your most valuable tool. If your viewer can't do this, upgrade immediately
Do you use a dedicated OTDR viewer or just the factory software? Let me know in the comments. Don't be the tech who closes a ticket