What would be the grammatical pro's if every country's official alphabet was the International Phonetic Alphabet?

The alphabets of many languages except English do a fair job of representing the sounds of the language.

For me, the IPA's strength is not standardization, It is the ability to transcribe speech accurately. If people wrote in the IPA as they actually spoke , there would be chaos. I think English would need about 50 characters to cover the sounds.

I took a course in transcription in the IPA at the Citadel in Charleston, SC. The first exercise was to transcribe our own speech. Despite our own varied accents, from our transcription, we thought we all spoke Midwestern English. The Charleston accent isn't even classified as southern. One must go a few miles north to Monks Corner or Summerville to hear "Southern." The real fun was transcribing the creoles in the sea islands.

People living on one island sometimes have difficulty understanding those one island over.

I have a friend, Mike Lentine, who writes dialogue poetry in the English alphabet but in various creoles. Some of the speakers are easy to understand, some not.

My native language is English, I am fluent in German and Russian. Both have undergone orthographic reform. I think English would benefit from something like that.

Grammar has nothing to do with pronunciation. The advantage is: if you know the IPA, and you transliterate words in any language into the IPA, then anyone else who knows the IPA can read them and pronounce those words correctly. This is why more and more dictionaries include the IPA transcription of the headword entries.

Grammar has nothing to do with spelling.