I do this to have a little record of my crafts, but there's also a more fun reason than that.
I am addicted to the swaps on Craftster.org and am always crafting stuff for that; I don't want my partners to get wind of until they receive it.
There's a certain type of stalking we swappers do. Any swapper worth their salt would probably be checking out their partners blog at least once during crafting time. I've had it happen to me, they posted what had been made before the package was mailed to me. Surprise was squelched!
So please, dear reader forgive me my old crafts and never fear,
I'll be posting what I make for swaps as soon as my partners post in the swap gallery! :D