Well, it's not that much vital but anyway. I have some .svg file (taken from the web and optimized a bit in nodes by myself) - like 10 contours with total of around 400 nodes. Filesize is about 21kB. Unfortunatelly, I need the original drawing resized to about 91% from original for my purposes. When I rescale it (doesn't matter as grouped, as "scale all together" and even scaling each contour separately and aligning back by hands) and save file it gets the size of about 32kB. The magical "clear defs" is performed, but ....
Anyone could advise how to avoid this increment of filesize?

If the original files have been taken from the web and aren't Inkscape SVG files, the increase in files size could be due to extra Inkscape metadata being added, or additional precision being recorded in the coordinates. Try saving as "Plain SVG" or "Optimised SVG".