Why typewriters will always be useful:
You are trained to think like a 20th Century writer.
When there is no backspace, words are more carefully chosen. When typing each letter requires more time and effort, sentences are more concise and meaningful.
On the surface, a typewriter slows down your typing speed versus a computer. But it also turns you into a better writer. As Nick Joaquin wrote: "It is not in how you use a tool, but in how a tool uses you."
Writing becomes a multi-sensory experience
The feel, the sound, the printed image of your work -- writing on a digital device feels 'soulless' in comparison. As humans, we crave physical as much as mental experiences. Writing can be both with a typewriter.
The writer's plague of our age are the endless distractions of social media.