People here might not realize, but your standard olympic plates can be off 3+ % up or down. this might not matter with 2.5s etc. But when you're benching 315 and planning on opening with it, but your plates are light you might be in for a rude awakening if your set is actually 306 and a local meet has plates that weigh heavy.
315 could easily be 306 or 324. My 45s weigh 14.5 pounds heavy total, when we have six on a side. I didn't weigh the 100s since they normally sit in a corner.
Or you could get calibrated Ivankos from Sorinex for roughly 4$ a pound. He has the best prices I've seen and the plates are guaranteed to be within 10 grams on fifty kilos.