Security. Documents produced on a manual typewriter cannot be hacked or downloaded, keep the document in a locked drawer and unless you give it to someone it is safe from those prying eyes.
Convenience. Your typewriter is always ready and you do not have to worry about the availability of a power source.
Unchanging. The typewriter will always be there and will remain the same. There are no endless updates to be done.
Longevity. A typewriter will last for many years and will probably outlast you if you look after it. I am currently writing on a machine that is over eighty years old. There is no requirement to update to a new model.
Focus. Using a typewriter allows you to focus on the task in hand, writing. There are no annoying distractions such as The Internet and endless notifications from various apps.
Education. You do not have grammar and spelling correction to constantly fall back on, you write what YOU write, nothing more nothing less, if you cannot spell something look it up in a small pocket dictionary before typing it, you will be surprised how much more easily you will remember it next time you use the word,.
Pleasure. Using a typewriter just feels nice. I love the clicking of the keys, the ringing of the bell and the slide of the returning carriage indicating that another line is complete.
Make it personal, sending a hand typed note or letter is a nice thing to do. The reader will read it warts and all and know that some human and personal effort has gone into creating it. Every typewriter is unique and every letter generated on a manual typewriter is itself unique, it’s like a fingerprint.
Instant Documents, no need to mess about with a printer that isn’ t working properly, just wind the sheet of paper out of the machine when you are done and that’s it, sign and send.
Thinking Time. A typewriter forces you to think before you press those keys, the marks on the paper are permanent and are there for ever, think before you make them.
Typewriters are cool and people are interested in them. If you use one often people will want to talk to you about it, they are a conversation starter.
You have an immediate physical backup of your work. Everything you have produced exists in a real, physical, analogue form, a fault on a server is not going to trash it..
Affordability. If you get in before everyone wants one a typev/riter can be bought for far less than a laptop or similar. Prices are rising as people start to appreciate these machines and they are not manufactured any longer so don't leave it too long before investing.
Appreciation. A typewriter may well be an appreciating asset. People increasingly like and collect these things. If it turns out not to be for you you can always sell it, probably at a profit.
Chill Out. Using a manual typewriter forces you to slow down and in today's world that is a good thing. People these days are just in too much of a rush, slow down, type a letter, enjoy the rhythmic "ping" of the bell and take time over things.
Going back to using carbon paper is fun. Type out your letter and hey presto at the end you have not one but TWO copies.
WiFi, Simple benefit this, you just don't need it, if it's unavailable who cares, not the person with the typewriter.
Aesthetics, Yes, this does matter. A vintage typewriter just looks nice, lovely black and white keys with chrome rims, shiny black enamel cover, fitted leather case etc. etc. Beautiful.
Crashless. A manual typewriter will NEVER crash and cause you frustration. These things just keep on working, year after year.
Viruses. Well, a lack of viruses at any rate. You will never have to worry about your manual typewriter getting infected by the latest virus, it will just remain the same, day after day.

Well, that's just a summary of my top twenty reasons for using a manual typewriter. Don't forget that if you want to it is still very easy to bring your worK into the digital world, a typewritten page is easily scanned to generate an editable . txt file but it's just not nearly as nice.

Original document typed on an Imperial "The Good Companion" made in 1939, serial number 2D237.

24th February 2020