Your post points out an interesting fact about ballroom lessons: you can't finish, you can only quit.
Lessons aren't oriented towards establishing a degree of mastery and then stopping, instead they are oriented towards eternal study and improvement. Yes, of course some people stop studying after they are comfortable and just attend parties from time to time and do fine. But that is not really ever the plan - or at least not your teacher's plan. Instead, those who are involved in dancing at the level of teaching tend to assume that students will eventually become enthusiasts who are not content to stop. Of course that is also better for business!
But the other thing to keep in mind is that the more you learn and the more awareness and experience you gain, the more options for study you will learn of. If you take the task of buying something, you can walk into a store and buy some plain versions of it, all packaged up to look very nice and well marketed. But if you are really an expert consumer, you don't pay any attention to the packaging, because you know the product. And you probably know of specialty suppliers where you can get something a lot more functional for a a better price. So it is with dance lessons - if you learn your way around the dance world, your options will increase a lot.
