I'd actually encourage everyone here to avoid classes. There has been quite a bit of controversy around instructors exploiting students for money or otherwise. The culture is a bit zany. And there's pressure to become an instructor which requires spending more money. But primarily, classes are inconvenient. Do it on your own and you can just roll out of bed and straight onto the mat, and 30 mins later you're done and set up for the day.
I have mixed feelings about this. I’d agree that most places that offer yoga aren’t all that great — just today I saw a photo of a local (NYC) yoga class and the teacher was teaching the posture (standing bow) all wrong and everyone in the class had seriously messed up alignment. And some of the corporate chains have been known to push people into teacher trainings. But there’s nothing like having a great teacher guiding you through things. I personally can’t imagine being where I am in my practice without all the teachers I’ve been lucky to have.
There are a lot of quacks around yoga, martial arts and other practices.
That does not mean practicing by yourself is a safe or healthy alternative.
If you can't find good teachers in your city, do something else. But please don't blame a whole discipline for the poor quality of teachers and students.
I don't doubt that an instructor who can interact with you will teach more effectively, I was just answering their question. I would say it's possible but very suboptimal to teach yoga or dancing with just words. Illustrations and video improve on that.
People come from all sorts of backgrounds, with different coordination and relationship with body. Classes bring clarity of practice with group. With long experience, words or pictures may be enough. Otherwise the practitioner may be confused.