Recently I needed to scan and mail multi-page documents. I have a rather simple scanner that can produce descent .jpeg files, but when combining into a document it sucks. Therefore I prefer to scan in 100% quality and then produce documents depending on my needs.
E.g. hereby some commands to put two scanned pages into a single .pdf document with 75% quality (reducing ~2.3MB images into ~800KB):
convert -quality 75 page_1.jpeg page_1_75.jpeg
convert -quality 75 page_2.jpeg page_2_75.jpeg
convert -page A4 -compress jpeg page_1_75.jpeg page_2_75.jpeg document.pdf