Epson Expression 800 User Manual page 22

In some instances, you may want to create a large file—such as when
you'll be enlarging a small scanned original in your application program
and want to retain a high image quality. In that case, you may want to
select a resolution between 1200 and 2400 dpi so you can enlarge it later
with good results.
In other instances, you may be unaware that your settings are too high for
your image. For example, if you're enlarging an image's size in SilverFast
Lite so the scanned file loads into your application already enlarged, you
may not need to select as high a resolution for a successful scan. Your
settings are creating a file that may be slow to process and burdensome
to your system resources.
If you move the resolution slider to a very high resolution for its size, you
see a message warning you that the software will be "interpolating" the
resolution you selected. This means that the software must add pixels to
your image to achieve the resolution you chose, but may not increase
your image quality. If you see this warning message, you may want to
lower the resolution setting.
Basic Scanning Page 22