I had a bad experience with this once. I was in E+ with spouse and lap child and was hoping for dual upgrade. One upgrade cleared (hooray), but it made more sense for us to stick together. I tried to give my first class seat to the middle pax who (a) didn't speak English and (b) did not want to be separated from his companion one row back. It caused quite a ruckus; we had to orchestrate a multi-row switch. Now, when flying with the family, I take myself off the upgrade list to avoid this.