Answering this questions will require a lot more space than what . I rather point you to the best references you can find in order to deeply understand the requirement for SSA.

First, start with Wikipedia so that you get familiarized with the basic structure and building blocks of SSA (Phi functions, ...). Then, move to this reference article published in 1991, which is a bit more hairy than the Wikipedia article.

If you want a more detailed document, though incomplete, read this book.
It covers a wide range of algorithms for constructions/destruction and also analysis.

Answering this questions will require a lot more space than what is provided. I rather point you to the best references you can find in order to deeply understand the requirement for SSA.

First, start with Wikipedia so that you get familiarized with the basic structure and building blocks of SSA (Phi functions, ...). Then, move to this reference article published in 1991, which is a bit more hairy than the Wikipedia article.

If you want a more detailed document, though incomplete, read this book.
It covers a wide range of algorithms for construction/destruction and also analysis.

If you wish a long/detailed answer, let me know so that I can write a proper one.