Ah, now this is an interesting thread.
Generally, I lack confidence in what I write so in order to combat this (or indulge it - you tell me) I tend to follow a set regime when writing sitcom scripts. Typed first drafts look the same as final drafts only less funny, so I spend as little time typing as I can. For me it goes like this:
- scribbled notes, gags and plot ideas
- scribbled plot outline
- hand-written treatment/step-by-step plot
- scribbled first draft scene-by-scene
- hand-written second draft scene-by-scene
- typed third draft
- revised drafts
That way by the time I get to typing the damn thing up it's at a stage where it could potentially get sent off (save for typos and a bit of re-editing). This is also one of the reasons why I take so long writing. It works for me though, which is the main thing.
However, with sketches (unless they take a bit of planning) I tend to work straight from the computer.