Previously, you'd have to download Android Studio or the SDK to get these, which are a 400MB-1.6GB download. Even the smaller command line tools download is still 200-300MB.

Having ADB and fastboot available outside of the other two main downloads, first of all, saves space. Android SDK takes up 292 MB of space.

The first thing you want to do is download and install the Android SDK if you haven't already. You only really need ADB and Fastboot (if you're unlocking) so you can skip the entire Android SDK ...