• You speak real English, not made up.
• You understand what they say to you in English.
• You learn vocabulary more quickly, because your mind needs to know how a word sounds to memorize it, if you don't give it the correct pronunciation it will make it up. The problem is that you will never hear an Englishman pronounce it that way.
• You form sentences fluently, because your mind has the right sounds to do it.
Our mind has managed to establish a direct and fluid connection with speech. But writing is very recent and does not have that connection, we do not think by writing, we think by speaking and then, if we need it, we translate it into writing. In other words, to learn an English word or form a sentence we need its sounds. And if they don't teach us their real pronunciation, we automatically invent our own, which then takes a lot of work to erase from our minds.