Performance as well as correctness. Looking at generated asm tells you what was inlined, which variables are stored in registers, whether your common subexpress

Performance as well as correctness. Looking at generated asm tells you what was inlined, which variables are stored in registers, whether your common subexpressions were optimized, etc. You can often tweak your C code to generate the assembler you want, without needing to actually write asm. This is especially important in C++, where you depend on the compiler's optimization ability a lot more.