[chubbnix]

The article mentioned how he intentionally crammed together everything to fit on a single unfolded page so they would not need to flip the page over. This article suggests the paper may have been free for Bach though, but I suppose that doesn't account for his time spent writing or rewriting his works. https://www.bach-cantatas.com/Articles/BachPaperSize.pdf

[siraben]

This was fascinating:

  And what about all the candles used to illuminate the parts? Not a single drop of tallow or candle wax or darkening due to the close proximity of a candle has been detected or reported regarding Bach’s original parts. Touching the parts while carrying them or turning pages would tend to leave traces, but these are not in evidence. Eventually these copies of the original parts would be collected and deliberately destroyed by Bach so that they could not be used to reconstruct the cantata.

[henryrp]

Another aspect of all old performance materials is the utter absence of rehearsal letters ("A", "B", "C" etc.), measure numbers, little eye-glasses ("watch the first chair here"), bowings, fingerings and all the other things contemporary classical musicians need to put into their parts during rehearsal. It really makes you wonder what a rehearsal in the 18th century could possibly have been like.

And yes, I'm pretty sure Bach saved as much paper as he could. The autograph score to the Christmas Oratorio uses spare staves all over the place. This is not a page-turning consideration. An aria may coexist side-by-side with a chorus for many pages at a time to evidently prevent those 2-3 staves at the bottom of the page from being wasted.