When scanning a paper, it is possible to use a lot of parameters within xsane. The output format can be chosen also, for example PNG, JPG or PDF. The outcome may be a PDF-file that is way too big, easily more than 10 megabytes for a single page. It is quite easy to transform it to a smaller file:
convert -density 200x200 -quality 60 -compress jpeg \
Unless you scan very often, it is easier to scan once with a relatively high resolution and then run this conversion with different values for quality and density rather than running the time consuming scan with different xsane settings.