While using Inkscape, I found some of my SVG files become very big like 1-3 MB. Trying to find a cure, I finally found out that we can use the
File>Vacuum Defs command to reduce the file size. After using this command my 1-3 MB files are reduced to 8-12 KB.
Below is quoted from Inkscape website...
"Many of the no-longer-used gradients, patterns, and markers (more precisely, those which you edited manually) remain in the corresponding palettes and can be reused for new objects. However if you want to optimize your document, use the Vacuum Defs command in File menu. It will remove any gradients, patterns, or markers which are not used by anything in the document, making the file smaller."
http://inkscape.org/doc/tips/tutorial-tips.html