As a part of our spring cleaning drive in our remote repo, we found and deleted a lot of leftover merged branches.
I wanted to find a quick way to do the same locally, and I happened at an answer, which I've written down below, to save it as a quick note for myself, and others.
Add the following to your git config by running the command
git config -e --global
[alias] cleanup = "!git branch --merged | grep -v '\\*\\|master\\|development' | xargs -n 1 git branch -d"
Now you can use
git cleanup; to delete all the local branches (excluding
development) which are already merged into the currently checked out branch.