300DPI is high enough to be clearly readable and results in much smaller files than 600DPI. The recently added BVWS bulletins such as this
https://www.bvws.org.uk/publications...letin_37_1.pdf are scanned at 200DPI for the colour and greyscale pages, and 300DPI for the bitmap/monochrome, which is fine for on-screen reading while keeping the file size down, but not really enough for printing.
Lower resolution is also faster with most scanners.
My approach is to scan to lossless image files (TIFF or PNG), do any tidying and cropping etc in Photoshop Elements, then import into PDF-XChange Editor for final PDF creation and optionally OCR. JPEG should be avoided for interim files as it is lossy.