Useful for many people, but particularly valuable for people who find typing a difficult, painful or lengthy process, including common ground between impaired motor ability, hearing loss, and impaired speech.
Pre-defined chat and emojis can also cross language barriers, which is why it was implemented in Star Ocean, allowing collaboration between Eastern/Western audiences.
This would be particularly powerful if combined with switch access and speech <-> text.
They can also be combined with other methods of communication, as already shown in Dragon Age 2’s icons attached to conversation options, or Battlefield 1’s simultaneous pre-defined message communicated as both speech and text.
An option to add additional custom messages would be helpful, and the presence of presets would also enable another use case; a parental lock to only allow sending/receiving messages that are constructed from those presets. This is a common approach in online environments aimed at or with a high proportion of children, such as Club Penguin and RuneScape.
Predefined text messages on Android