I found the topic a little vague. are you asking about sending a letter, regardless of how it's written (typed, printed, hand written, etc..) or send a hand written (with pen, stylus, pencil, crayon, quill, etc..) letter?
I try to include a 'year in review' letter with our Christmas cards every year. I write them on the computer, attach photos, etc.. make it all nice & pretty. And, because my hand writing absolutely sucks!!
I remember my mum "forcing" my sister & I to write thank you cards for gifts & such. We hated it. But, I see the reasons why now, and understand the importance. Sadly, I don't do it as nearly enough as I should.