Let me expound on my previous statement. As a full scale pilot, I use trim tabs for two reasons. Trimming the airplane reduces pilot fatigue and workload. Because our models aren't controlled with a yoke and flight pedals that weigh 40+ pounds (because of massive aerodynamic forces) physical fatigue isn't an issue; however, reducing pilot workload is always a worthy cause. Humans are notoriously poor multitaskers. Every time we focus on a task (such as pulling on the yoke to maintain level flight) we lose our ability to do any other task concurrently (plan a descent, talk on the radio, read a chart, or watch for other aircraft). Therefore, it is in our best interest to remove any extraneous tasks, such as the need to maintain level flight. We do this by trimming the airplane until thrust equals drag and lift equals weight.

There are times where trimming is counterproductive. Say I want my model to descend/climb. I wouldn't want to simply raise/lower the elevator trim for two reasons. The first reason is that I am going to pick up/decrease airspeed, which will require progressively more trim to maintain descent/climb. The other reason is that I can simply lower/raise the throttle slightly to achieve a more uniform and non-accelerating/decelerating descent/climb. Nor would I want to trim the airplane for a turn since I will not be maintaining my control setting for more than several seconds. But if I trim for straight and level flight at my most common power setting I end up with a very neutral aircraft that can maneuver smoothly and without excess input, which would rob me of time to think about the maneuver my model is in or other models in the area to avoid.

I suppose that is my rationale for teaching new R/C pilots to trim the way I do.