More than just a parlour trick, teaching your dog to sit is a great way to affirm your position as pack leader and is useful in keeping your dog out of potential trouble.
For conformation during shows and trials kennel associations in many countries group breeds based on the purpose for which the dogs were originally bred. Although there is not an international standard for group titles, e.g. the Rottweiler is part of the "working" group in America and Canada, and the "utility" group in Australia and New Zealand, the breeds within each group are largely the same, regardless of the their titles.
The first thing that's required for a dog to respond to any command is for it to know you're addressing it, and that starts with a name.
A fantastic series of dog posters illustrated by artist Lili Chin.