The website is a great list of features, and a valuable resource. It’s a lot like Apple’s privacy page, where each feature is described in easy-to-understand language.
In an iPad Diaries entry, Federico Viticci describes how he uses Type to Siri on his iPad Pro as a sort of “smart command line.” Type to Siri is a feature introduced in iOS 11 and macOS High Sierra. Although billed as an accessibility feature, it lets you type to Siri instead of talking. This can be helpful if you’re in public and you feel awkward talking to your iPhone. On iPad and Mac, it might even be more efficient to use Siri this way, since these devices have keyboards. Since you’re typing rather than talking, it could even be a bit better since there is little room for Siri to misunderstand you. To make it faster to use, Federico created specific text shortcuts for commonly used commands.
It’s useful for people who may feel awkward talking to their iPhone or Mac, and helpful in certain situations where silence is a virtue, like in a library.