I actually had a case like this earlyish in my career. I had a job where my main responsibility was maintaining and developing large ETL scripts for an online book store (so hundreds of millions of rows). We had one script which did the meat of the work which was running many hours each night. My job was to speed it up. Watching it run for a bit, it occurred to me to wonder how long it took to send each line of progress info (couple of lines each for every single row) to the log. I remember my boss at the time didn't believe me. "I think it's logging," I said, and turned logging off just for funsies. Boom, 100x faster.