I do teach my students to use the rudder. For one thing, on some model planes the ailerons aren't very effective at low speeds, so it's good to have a backup. The SIG LT-40, wonderful as it is, is subject to this, especially if it's a little nose-heavy. And when people get good enough they will want to coordinate turns, especially with large models, and do things like stall turns and slips, all of which which require rudder.

What this thread was originally about, however, was crosswind landings, and for those I teach my students to crab. Telling people things like "just use your rudder instead of your ailerons" isn't going to help a beginner who has trouble with crosswind landings.

It would probably be a good thing if someone with better computer skills than mine could contribute some diagrams to illustrate crabbing. Diagrams with motion would help a lot. Picture is worth ....