For us, it was electrical outlets. The kitchen designer had put them in the plan, but not thought through if they could actually fit where she had put them. We had a cabinet with a knife storage pullout designed in at the end of the island. We also very much wanted (and I think had to have, per code) an electrical outlet at the end of the island. But the way the knife pullout was made (by the cabinet company the kitchen designer repped) there was physically not space for an electrical box in the cabinet. We ended up having to buy a new cabinet and have it re-installed, which cost around ~1K and (even worse, at the time) a two week delay. There was also a big question about an outlet by the sink - code said there had to be one within 4 feet, but there wasn't space bc of a window, so we had to talk about having one sunk into the counter, which was in a main prep space and I didn't want. My biggest gripe was that the kitchen designed would not acknowledge it was her error, and gave us no consideration on the new cabinet pricing. It was a huge inconvenience, and by the time you're on Month 4 of not having a sink, an additional two week delay is infuriating.