Updating Sitemaps

I have a quick question....how often should you update your sitemap in Google. I know the vbseo sitemap is automatic, but I have written a very small one for my online videos and i manually update the file when i put up a new video.....should i resubmit after every added url??

Thanks

once i had read some forum discussions about this...i dont think, you must update and re-send it google after every additional URL.i think one or two times per week is enough...so , google does not indexing a website via sitemap...sitemaps only help google seeing your site's category,url,section etc hierarchy more easily.