There are a lot of different opinions about Charles-Louis Hanon's "The Virtuoso Pianist in 60 Exercises". Some say it is unmusical and can even lead to wrist damage, while others think they are the best exercises around. I am a beginning piano player — how should I regard these exercises?
There are several schools of piano teaching. I have been raised in the idea that almost all technical training should be done with a specific piece of composed music as a target, not in isolation, and should be defined by the teacher after observation of a student's playing. It does not take long to write down a little exercice on a sheet of paper. The art of teaching is to propose gradually challenging piece from the repertoire while covering the most important technical ground.
Chopin and Liszt were the first piano studies which were also works of art by themselves and had a vision wider than the style of their time.
Clementi, Hanon, Kunz, and consorts are in my little teaching experience a very good way to put off students and not achieve anything worthwhile. But other school of piano playing may have an efficient tradition of using them for the student's good. I do not know how to do that. I know how to do that with Bach, Schumann, Debussy, Scarlatti, Bartok, Chopin.
Czerny is something else, I would recommend some of his studies from his pedagogical works, but again according to what you desire to be able to play and with a grain of salt.
Studying too much (and too soon) without pause, regularity and progressiveness, denying the pain, believing that forcing and striking hard will give you better fingers, is the most common and real source of wrist dammage, hand inflamation and traumatism, not a specific set of piano exercices.
Integrating over what I've read (and I am not a pro), I would be cautious unless you have a teacher to catch you if you are at risk of hurting yourself. Still, I also suspect that it's hard to hurt yourself unless you spend hours at a time with bad hand position.
A truly wonderful book ("Playing the Piano for Pleasure") recommends them.
I would like to preface my full response by saying that I detest those exercises. They are boring, repetitious, and, towards the end of the series, just really freaking hard. On the other hand, they do a reasonably good job of isolating specific "riffs", and building confidence in playing them.
Their place in my musical development is as a tool to help me train my fingers in playing technically difficult passages within "real" music (for want of a better term). For example, when I'm having trouble playing parallel octaves, I break out the octave exercises that are similar to the section giving me trouble. When I'm playing through the Hanon exercises, I also transpose them into the key of the target piece, rather than staying in C major.
The point is, I like them for helping me play specific passages. Playing through the entire book in one marathon session is not useful for me. That being said, doing so is probably not intrinsically harmful to your playing.
I would like to answer this question by quoting a musician I met online. I forget who it was, so I apologize for it. But that person developed carpal tunnel from hammering away using similar excersises. However, what he said afterward will stay with me forever. He said, "These excersises really work in helping you develop better playing skills. Just use caution and think of it as lifting weights. Very helpful, but you can hurt yourself."
I believe that quote highlights exactly what these excersises are designed for. To use a similar analogy: Imagine a boxer lifting weights. That in itself does not directly make them a better boxer. But it will allow the boxer more strength, power, and stamina in the boxing arena. For a pianist, these excersises are designed to give the player more finger strength, better flexibility, and greater accuracy. However, you should think of it as a tool and nothing more.
Just like the professional boxer, you do not want to spend your entire practice time lifting weights. A boxer that does only that will get murdered in the ring. The boxer will have plenty of strength, but no boxing form. Conversely, as a pianist, you need to develop a strong musical sense. These excersises will not teach you how to interpret music or play "beautifully".
A little off topic: It is the same issues with people who depend entirely on the metronome. It is an excellent tool for keeping in time, but you still need to develop your "internal tick".
Just remember that there was a time in which these tools did not exist.