That depends on a lot.
For a bodybuilder, chasing weight numbers is dumb. What's the point? Plus the chance of injury is heightened. To have a great bodybuilding workout, you can get away with very light weights. It's all about intensity, right? So, if you load on some plates, it's pretty irrelevant if the numbers stated on the plates are out by 250g. Or 500g. Or, like most cheap discs, out by 1kg. It doesn't matter. You just work the weight until you hit exhaustion, or beyond.
But, if you are an olympic weightlifter, or a powerlifter, or, to some extent, a strongman competitor, the actual weight is important. In fact, in competition it's everything. So if you are in a gym and using a shit bar and a shit set of plates that are all out by, say, 500g, then if you were training with 220kg you may end up being 5.5kg short. So? Well, world records are set or missed by as little as 1kg for weightlifting, and just 500g for powerlifters. So hitting your numbers accurately is important.
You will find that serious competitors in weightlifting and powerlifting use calibrated plates and bars. Even the collars are calibrated.
Bodybuilders? Waste of time using calibrated gear. Weightlifters and powerlifters? Pretty important.