They pretty much need to be frozen or destroyed if multiple eggs are retrieved during an egg retrieval procedure for IVF. You only implant one embryo at a time, so if you collect 8 eggs during the retrieval you’ll potentially have 7 viable embryos that need to be dealt with, for example.

They fertilize each of the eggs that were retrieved and observe their development over a few days. Some will not develop well enough to be considered for implantation into the uterus, and they basically need to be destroyed as they have no hope of developing past a few weeks at most.

They’ll use the most promising embryo for implantation. The remaining good quality embryos can be implanted at a later time, either if the first embryo doesn’t work out or years later if you decide to have another kid. You can pay to have them frozen and stored for the next time you need to do IVF (which saves a ton of money on your next round of IVF since you don’t need to pay for the medication or egg retrieval procedure), you can donate the embryos, or they can be destroyed.