Assembly language has several benefits:

• Speed. The fastest programs.
• Space. The smallest programs.
• Capability. You can do impossible things with MASM
• Knowledge. Know assembly language = know your computer

With your MASM knowledge, you can optimize your algorithm better than /O1, /O2, /Ox.

I found this good article from Paul Hsieh Assembly LAB : Human vs Compiler optimization. Please read.