The first thing I have to think if I want to reinstall instead of upgrade is, how to backup MacTeX & homebrew. I have to consider if it will generate pdf documents correctly. (MacTeX is installed in /usr/texbin/) Reinstalling MacTeX is not that hard compared with reinstalling homebrew. Homebrew, though bottled most package, will take a long time compiling a version gcc with openmp support, let alone recalling who to install. And gcc is not the only thing that need a compiling job. Maybe, years later, I will follow the path of reinstalling or moving back to Linux.