Imagine if I asked you to read English words in this way. I segment the words into individual syllables, and show you one at a time. You read each one aloud, and then (very quickly) I show you the next one. So you're constantly reading the phonemes. At the same time, you try to listen to yourself and turn the sounds into meaning.

That's kind of what it's like for me to read pinyin. Pinyin is great for learning pronunciation, but not great for getting meaning: it's just too slow.