The following is an excerpt from Ziyuan Yao's free ebook Breaking the Language Barrier: A Game-Changing Approach. The excerpt provides an in-depth analysis on how PIE helps an ESL/EFL learner to acquire both a word's pronunciation and spelling.
Why PIE?
To learn a new word, two tasks, among others, are involved: learning its pronunciation and its spelling. These two tasks are related, and choosing which to do first makes a lot of difference. If we learn spelling first, we'd be memorizing a (usually long) sequence of letters, which is as tedious as remembering a long telephone number. But if we learn pronunciation first, we'd be memorizing a much shorter sequence of syllables, which can be done in a breeze; then pronunciation can serve as a good catalyst for the subsequent memorization of spelling.
Therefore pronunciation plays a prominent role in word acquisition, and it is worthwhile finding out a good method to learn it.
A big drawback of IPA is that, because it shows pronunciation separately from spelling, it gives the user a chance to skip learning pronunciation at all. This is especially the case when the user encounters an unknown word in reading an article: at that moment, the user cares most about the meaning of that new word, not the pronunciation, as he doesn't have a need to hear or say that word in real life in the near future. Therefore he is very likely to skip learning the word's true pronunciation in a dictionary, but instead assume a pronunciation on his own. Assuming a pronunciation will then lead to two new problems:
PIE, on the other hand, eliminates the problems discussed above. Correct pronunciation is made immediately available to the user as he scans through a word's spelling; there is no need to assume a pronunciation at all. The user will memorize the correct, complete pronunciation firmly, which in turn will facilitate memorization of the complete spelling.