For me it's my own private gym and I have 14 45s, 4 100s, and assorted 2.5s, 5s, 10s, 25s, 35s, and two bumper 10 kilos. I take the weight on the bar as my log weight, but it is not to hard to weigh my stuff and mark them.
It was curiosity and such getting to me since I was to close to 600. But my big point applies, if you're going into a meet with calibrated plates, it is good to know you were lifting a little heavy in the gym. This could get you 20-40 more lbs on the platform.
Say you are squatting 550, but it's 12 pounds heavy, and you dl 610 and it's fifteen heavy, and you bench 320, but it's 10 heavy, you have 37 lbs there. Choosing a final attempt 5 kilos heavier might be in the bag.