Speed reading can be valuable for those who read one word at a time.

The techniques involved in reading groups of words and, sometimes, entire sentences, will result in more speed.

However, there is a limit. Once you get over 500 words per minute, or so, there is a distinct possibility that you will lose the facts of what you are reading.

This has been shown to be true in several tests on people who read very fast. The do get the essence of the book/magazine/article, but, the details cannot be repeated accurately.

It all depends on what the material is. If you are reading for pleasure, the faster you can read, the more pleasurable it will be. Retaining the details of a novel is not all that important.

But, if you are reading non-fiction, such as a dossier on hydrocracking of oils, you are not going to read such an article at 1000 words per minute and retain much of it, IMHO.