If I ever have to start completely over with my install, I would consider putting /usr/local on a separate partition.
Going back to the early 1990s I have been a fan of partitioning. In MS-DOS I had three partitions, a C:, D:, and E: partition. System stuff went on C:, applications on D:, and I used E: to store all of my data files. I continued that basic strategy into Windows. Keeping all of my data files on a separate partition has always saved me much grief, especially back in the days when I tended to tinker a lot more than I do today. I could reinstall software to my heart's content and never touch my data.
When I started tinkering with GNU/Linux a few years ago one of the first things I learned was to divide my hard disk into partitions. This saved me much time in the beginning because I was flirting with several distros and with the partition scheme I did not have to reinstall a lot of files.
Currently I save all of my custom-made bash scripts to /usr/local/bin. I also installed all of my TrueType fonts in /usr/local as well as many system event sounds (I use KDE). This partitioning scheme will save me time once again in a few weeks as I install Slack onto another box. I'll simply copy the files from usr/local and be done.
I also use a dedicated /boot partition, which allowed me to play with several kernels when I was playing with several distros. I have all of my GRUB files installed to /boot and I need only edit the one config file when adding a new kernel to test.
I use a dedicated /home partition and never have to reinstall anything there either. My /opt directory is on a separate partition and this helps when updating KDE or other third-party software.
Some people don't care for the extra up-front work with partitioning, but once one gets the hang of things the idea is one of those that simply makes sense for a lot of people. At least for me---YMMV.