At some point in your martial arts training you will be asked to teach. It may happen easily enough, by helping a junior belt learn their next attack, defense or other technique. The business model of martial arts is like none other. I cannot, for instance, imagine frequenting a pizza parlor only to have them (after a while) ask me to cook my own; and then a little later on, ask me to cook for someone else (with the proprietor keeping the proceeds). Eventually, I'd be scheduled several nights a week, assisting the other cooks, and occasionally delivering hot pizzas, subs, and wings to regular clientele - for no pay. In fact, I'd still have to pay for my own pizzas! Alas, this is martial arts.
The first several times you're asked to teach, it is an honor - and it should be. You will have demonstrated sufficient mastery of the material (at what ever level you have attained) such that others feel you can be trusted to accurately relay the material with judgment and nuance. Terrific. Congratulations. Maybe, over time, you'll find yourself teaching more classes than taking classes. At some point, you're going to wonder why you're still there; paying tuition while teaching. To the uninitiated (a.k.a. anyone who is not teaching), you are now a teacher, with all of the respect, responsibilities, and salary that comes with it. Not bad if it were true.
To be sure, you have responsibility, and if you're any good, some respect. The whole salary thing? Not so much - you're still paying just like everyone else. So why not complain. Why not go to the owner/master and say, "Master, I came here for a workout and to learn a martial art. I cannot progress if I'm teaching all of the time." What's the master going to do if you confront him? Cut your pay? Reduce your hours? Tell you to go away? Not likely. But, before you walk out and find another school, make sure you understand the whole picture.
I have known any number of practitioners that have become reluctant teachers; some have done well, some have enjoyed it, while others have become disenchanted and moved on with their life's work. In every case, there are two things which have been true; one positive, one negative - and the negative one can be controlled.
First, it is definitely true that the teacher does not get as much of a workout as the rest of the class. If you joined a martial arts school to get a great sweat-rendering, fat-busting, muscle-burning, age-defying workout, then you will likely see a drop off as your teaching schedule increases. This is the #1 complaint of karate/judo instructors; they just don't get the workout they did as a student. I'm not going to argue the point, but I will say that the teacher has a great deal of control as to whether they get no exercise, a little, or a lot. I sweat every class I teach. I have had other instructors comment that I sweat more than my students (my students vehemently disagree!) But the point is that the instructor can get some workout, even while teaching - maybe it's not the back breaking bone killer you're used to, but it's still a workout.
The upside to teaching is that your martial art techniques tend to improve exponentially. If you came to class 3 days a week for two years you would expect some level of improvement in your stance, your attacks, your blocks, kicks, timing, and feints. As an instructor, these will improve faster than they would as a student. As an instructor you will only perform/practice your techniques one tenth as much as the rest of the class, but your practices will be highly concentrated. As you demonstrate a technique you will be concentrating on the exactness of the movement, balance, extension, flexibility, aim, power, recoil, stance, and timing. You will also be aware that everyone is watching you for instruction.
As you correct your students you will be seeing slight variations of form that make a significant difference in execution. Your physical demonstrations, verbal reiterations, and visual observations will continually reinforce proper form, understanding, and ability. Your growth as a martial artist will accelerate rather than stagnate. I've seen this time and time again. I've heard other instructors comment that their kicks got higher, stronger, and faster once they began teaching full time. It makes sense once you think it through, but the conventional wisdom says that practice makes perfect and more practice make more perfect (yeah - I know, the double use of 'more' doesn't work but it sounds like it should, and besides, you know my point).
But practice doesn't make perfect - practice makes you very good at repeating whatever you practice. Practice poorly and you'll get very good at executing poorly. Practice less, but with more effort, concentration, precision, and attention to detail and you'll get very good. So, if you want to get better... Teach!