I sort of have to.
The stages of making my videos:
1. Write script (Proof read, make corrections)
2. Create cartoon (Takes quite a while)
3. Put them together in Sony Vegas
4. Once everything is together, REFINE REFINE REFINE.
It usually takes between 1 and 3 renders to get the video the way I want it.
I don't think script writing is necessary in the slightest. It gives a less natural feel to the video, especially with comedy. Improvisation is always more fun.