The case for reducing the size of SVG is the same as for any kind of web asset: it reduces the initial transmission time (and improves the likelihood of a cache hit) and so reduces the time taken to load the page.
I doubt if it's worthwhile squeezing the last couple of bytes of gzip compression out of an image (other than as a fun and informative exercise), but when programmatically generating SVGs it's easy to do so naïvely and in these cases you can get big savings in file size. Here's a worked example where I was able reduce a generated image to about 17% of its original size through simple fixes: http://garethrees.org/2013/08/02/svg/
Similarly, tools like Inkscape need to represent information for editing the image (such as its layer or grouping structure; or style information maintained on a per-object basis) which is not necessary for displaying it, and this can amount to a large proportion of the SVG file size.
I doubt if it's worthwhile squeezing the last couple of bytes of gzip compression out of an image (other than as a fun and informative exercise), but when programmatically generating SVGs it's easy to do so naïvely and in these cases you can get big savings in file size. Here's a worked example where I was able reduce a generated image to about 17% of its original size through simple fixes: http://garethrees.org/2013/08/02/svg/
Similarly, tools like Inkscape need to represent information for editing the image (such as its layer or grouping structure; or style information maintained on a per-object basis) which is not necessary for displaying it, and this can amount to a large proportion of the SVG file size.