Homebrew size of Cellar

The Cellar contains what homebrew installs. It then creates symlinks in the /usr/local/bin directory to the files in the Cellar. If you delete what is in the Cellar directory you'll no longer be able to use the stuff homebrew installed.

The cellar directory contains all the packages that homebrew installs. However it also contains every version that you have installed.

You can run brew cleanup to remove old versions of packages to clean some space.