The case study here is why Chinese is so hard for native English speakers. One of the many reasons is Pinyin. In the long run, Pinyin really sucks.
For zero beginners, Pinyin makes Chinese accessible and approachable. People can get a hang of it quickly, and be able to speak some basic Chinese without the knowledge of characters. It is really a handy tool. But if anyone wants to successfully go pass the beginner level, they have to resort to learning Chinese writing system.
Here is the detailed analysis on how Pinyin sucks.
First of all, Pinyin is very confusing. That so many Chinese characters have the same or similar pronunciations leads to so many Pinyin syllables look the same or are with minor differences. If one reads scripts written in characters, the meaning is very clear. But if the same scripts are written in Pinyin, extra effort must be made to decipher the meaning.
Secondly, students cannot ground meanings in Pinyin, as they can do so with characters. For example, 事and是, the Pinyin syllables are the same. With one glance on the two characters, one knows the meaning clearly. But looking at Pinyin syllables, no one knows which is which.
Lastly, Most people know that Chinese characters don't give clues on how to pronounce them. Worse than that would be that Pinyin gives fixed pronunciations, indicating clearly on the pitches and tones, while it fails to reflect variations of pronunciations and tone changes in natural speeches. Relying too much on Pinyin gives a false impression that there are "correct pronunciations and tones". This concept of "correct pronunciations and tones" is so misconceived. It is a misconception so readily and willingly accepted by many, and wide spread through Pinyin.
Also, Pinyin gives the wrong impression that all Chinese people speak according to one standard tonal script. And of course, they don't. Regional accents are real and fun to spot. A person with a Shandong accent speaks differently with a person with an Anhui accent. Neither of them speaks according to the standard Pinyin. If we pick 100 people randomly from China and ask them to read aloud 水餃and 睡覺, we probably hear 100 different pronunciations with slightly different tones. And watch it in awe, they probably can communicate without any problems!
The point is that it is fine to start with Pinyin. It is good clean fun to try to differentiate "dumplings" from "sleep", or "buy fish" from "sell jade", as long as it is happening inside classrooms. Pinyin does not translate well outside of classrooms.
In the long run, Pinyin creates more huddles than bridges.