Writing by hand necessarily introduces an additional editing and review phase that wasn't there before.
When typing posts from scratch I would really only be performing a final check for grammar and errors whereas transcribing from paper to screen forces me to re-read and re-evaluate what I have written.
Occasionally, I'll redo entire sections as I look upon things with fresh eyes, there being a delay between the initial writing and transcription. However, there usually aren't too many changes but I do find myself catching a few things that I might otherwise let slip.