If your website structure has remained almost the same, and you have not added a lot of new pages to that, there is actually no need to re-upload the sitemap and resubmit it because Googlebot looks for newly added contents to the websites and if there are no major changes, so why would you resubmit it and then tell Google to download it again? XML sitemaps should reflect the latest major web modifications.
As an example, if you are currently running a blog which has only a few pages and have installed the XML sitemap maker script on it, and then within a couple of days you post dozens of new content pages and publish them on your site, there will be a great purpose to tell Google. In such cases, if you edit the XML sitemap, uploading that and resubmitting it would be a great idea.