This guide is for discord.py 1.7 version. In upcoming v2.0, Webhooks were greatly overhauled and in fact simplified a lot. They no longer require adapters. Usage of webhooks is now quite straight forward. As such, this guide is now outdated and should not be followed.
Furthermore, this guide is focused on discord.py. No support for forks are covered in this guide.
Webhooks are a great way to send messages to Discord without having a bot account. You just need a webhook URL and just do a POST request on that URL and the message will be sent to discord.
Webhooks can also be used if your bot has to send messages to a channel a lot. For example, If your bot has event logging so everytime having to fetch channel and sending can be slow so you can use some webhook magic.