Also something to consider is that you don't need to re-submit the sitemap ever whilst your sitemap is in the same location and has the same title it always did. Google will on a regular basis fetch that sitemap without resubmitting.

I would say update the sitemap if you've a new page or deleted it - but its not a huge issue really if you are out by a day or 14 - unless your site is very busy with lots of visitors it's not that important to google, also I find they prefer natural crawling and finding than being told there is one new page - this said a whole section change is definitely worth updating it.