High-speed reading is a technique, and as with all techniques, it has its uses and limitations.

For reading, generally, I strongly recommend Mortimer Adler's classic How to Read a Book, itself an HN perennial, see https://news.ycombinator.com/item?id=12209446 (or all: https://hn.algolia.com/?q="how%20to%20read%20a%20book").

If you're trying to determine what to read, or want to rapidly get an overview of a book, or are "visually grepping" for specific content, then the tricks of speed-reading, especially of chunking, skimming paragraph ledes, and not vocalising or subvocalising, help.

If you're reading for deep understanding, you'll want to fully absorb the material (and work through the exercises!), though this can also involve several passes -- for textbooks or nonfiction, I'll scan the ToC, and then the chapter (especially for section/subsection titles), then read through in full.

Treating such reading as an inquiry rather than simply as data transfer helps tremendously.

And of course, if you're reading quality literature or poetry, you'll want to savour the language, words, rhythm, meter, and rhyme. Go slow. You'll appreciate it all the more.

Reading plays or dialogue-rich content is a particular skill -- try reading with different intonation or to sort out what possible alternate meanings might exist. Shakespeare is of course excellent for this, though many other plays (or film screenplays) are as well. Realise just how much latitude the actor or director has in translating from words on the page to those uttered on the stage or screen.