I came across this piece by Rean John Uehara in his blog and I immediately knew what he meant.
Why should designers learn to write?
It is good to write things you know because:
When you write, you share
When you share, you help
When you help, you make the world better
When the world becomes better, living becomes easier
Living easily means more happy people
Happy people are inspired people
When people are inspired, they share
And what they want to share, they write