The other day I was drawing an island, and I had a symmetrical countertop. Whenever I am dealing with something that is symmetrical, I like to chop it in half, draw one side, and then mirror that half on the other side. This is a really efficient modeling technique. What if you want to change the thing you just modeled later? Do you chop it in half, fix it, and then mirror again? You could, but this takes time and is tedious. I like to use components to make this happen automagically. Check out this video to see how I do this when drawing a countertop.
Kitchen Design Plugin for Sketchup, Sketchup training.