It certainly gives me peace of mind to know that - to a certain extent - my affairs are in order, so what I want when I go is recorded. The house is still chaotic, but my solicitor knows my wishes.
I'm 48 and if I was told I had a month to live I could look back now and think "Wow, I had a damn good life and I certainly didn't waste it!" I would like to be able to think the same whenever my time comes in the future.
I say this is a sad thought because generally death comes to most peoples' mind when they are going through hardship, poor health, loneliness, sadness etc.
ttfn is right. As you get old and realise you have only a short time left, getting shorter every day you have to face it logically. Also, even the time you have speeds by more and more quickly. Seize the moment is the right way to think of it and enjoy every bit of life that you can. You won't enjoy all of it, but you have to accept. I nearly said but that's life!!