Utilize one (of many possible) improvisational exercises to refine our play/scene/etc.
At any point in the process.
I find this particular improvisation more useful at the midway or further point. At the very least, I prefer it after a complete first draft -- however bad.
Other improvisations -- and indeed this one -- may be useful at other points in the writing process.
There are many improv based exercises in theatre. The field seems to rely and trust in the ability of its artists to be creative, witty, and funny on short notice and without pre-planning (or, sometimes, in spite of pre-planning).
This particular exercise forces a particular limitation on the props and scenery that the writer is allowed (and encouraged) to employ: only chairs.
NOTE: If you have trouble with "letting go" and experimenting, feel free to set a time constraint (as in the "Speed Through" exercise) to rewrite the portion you're attempting to rewrite. Whatever you think is enough time to write it in... divide it by 4.
Hopefully this exercise gave you the opportunity to separate from the rigidity that may have dominated your perception of your work (and perhaps even caused a "block") and allowed you to work on a different problem (that of chairs) and come up with new and interesting decisions that may inform your play in subsequent drafts.