It depends, if your docker installation uses /var, it will surelly help to keep it separated.
For my home systems, I have: UEFI, /boot, /, home, swap.
For my work systems, we additionally have separate /opt, /var, /tmp and /usr.
/usr will only grow when you add more software to your system. /var and /tmp are where applications and services store temporary files, log files and caches, so they can vary wildly depending on what is running. /opt is for third-party stuff, so it depends if you use it or not.