• they enhance the portability of the compiler to other target processors
• Bprogram analysis is more accurate on intermediate code than on machine code
• Cthe information from dataflow analysis cannot otherwise be used for optimization
• Dthe information from the front end cannot otherwise be used for optimization

Performing optimizations at the machine-independent intermediate-code level (rather than on final machine code) keeps the optimizer reusable across different target architectures — enhancing the compiler's portability, since only the code generator (not the optimizer) needs to be rewritten per target.