Is Writer's Diary Useful?

There are always opposing opinions about these. Some people say it's totally pointless, while others swear by it. Here is what Virginia Woolf thought: ...I got out this diary and read, as one always does read one's own writing, with a kind of guilty intensity. I confess that the rough and random style of it, often so ungrammatical, and crying for a word altered, afflicted me somewhat. I am trying to tell whichever self it is that reads this hereafter that I can write very much better; and take no time over this; and forbid her to let the eye of man behold it. And now I may add my little compliment to the effect that it has a slapdash and vigour and sometimes hits an unexpected bulls eye. But what is more to the point is my belief that the habit of writing thus for my own eye only is good practice. It loosens the ligaments. Never mind the misses and stumbles. Going at such a pace as I do I must make the most direct and instant shots at my object, and thus have to lay hands on words, choose them and shoot them with no more pause than is needed to put my pen in the ink. I believe that during the past year I can trace some increase of ease in my professional writing which I attribute to my casual half hours after tea. Moreover there looms ahead of me the shadow of some kind of form which a diary might attain to. I might in the course of time learn what it is that one can make of this loose, drifting material of life; finding another use for it than the use I put it to, so much more consciously and scrupulously, in fiction. Have you ever tried it? Have you found any useful material for fiction from your diaries?