Here is how to save lots of space after multiple brew updates.

r2d2@starfighter:~ $ brew cleanup

Removing: /usr/local/Cellar/go/1.9.3… (7,652 files, 294.0MB)
Removing: /usr/local/Cellar/python/2.7.14_2… (6,344 files, 87.6MB)
Removing: /usr/local/Cellar/kubernetes-cli/1.9.2… (172 files, 65.3MB)
Removing: /Users/r2d2/Library/Caches/Homebrew/go-1.9.3.high_sierra.bottle.tar.gz… (89.4MB)
Removing: /Users/r2d2/Library/Caches/Homebrew/kubernetes-cli-1.9.2.high_sierra.bottle.tar.gz… (14.9MB)
Removing: /Users/r2d2/Library/Logs/Homebrew/wget… (64B)
Removing: /Users/r2d2/Library/Logs/Homebrew/go… (64B)
Removing: /Users/r2d2/Library/Logs/Homebrew/awscli… (64B)
Removing: /Users/r2d2/Library/Logs/Homebrew/sqlite… (64B)
Removing: /Users/r2d2/Library/Logs/Homebrew/imagemagick… (64B)

==> This operation has freed approximately 551.2MB of disk space.