If cooking fish, which cooks quickly and can overcook quickly, I put it in after guests arrive and have begun a beverage.
For something that bakes and takes long and where timing is not so delicate, I’d preheat and put the item in the oven before guests arrive.
For cookies for dessert, I’d have them ready on the pan, but place in the oven when clearing the main course. I also pre portion ice cream in the freezer and have coffee pot ready to press a button.