If you are entering a competition, then presumably you have practiced the schedule of maneuvers often enough to have it committed to brain memory and muscle memory. From that point of view, you don't need a caller to call out the next maneuver for you. But... people do sometimes get rattled when flying in front of judges, so having the maneuvers called out for you can help calm the jitters, allow you to concentrate better.

The rules may vary somewhat from one meet to another, according to the Contest Director's discretion. However, there are some rules of etiquette that are never out of place. I always ask the judges if they're ready for me to take off. In the days of scored take-offs and landings, I always announced the beginning and end of take-off and landing. Some flyers like to make these announcements to their caller, and have the caller repeat them to the judges. I like to announce my free downwind trim pass as well. Any exit from or entry into the box must be announced. Also, you should ask the judges if it's OK to land, since there may be another model setting up an approach on the same or an adjoining runway. And of course you should immediately announce loss of power or loss of control. And finally, when your model is back on the ground, thank the judges.

I can say that when I have sat as judge, I've always appreciated hearing either pilot or caller announce each maneuver loud enough for the judges to hear. It frees the judge and scribe to concentrate on their particular responsibilities--judge to keep his eye on the flight at all times, scribe to get the scores recorded accurately.

As you get up in the higher classes, occasionally fly in a class for which your practice is rusty, or fly Unknowns, the caller becomes more useful, even indispensable. So it's good to learn how to make the best use of a caller. If you're calling for another pilot, do your best to accommodate whatever he asks.