Sitemaps are the blueprints of your website for the Google Bots. This has become a protocol to help search engines crawl your website more intelligently. Before preceding, I would like to list that there are two types of Sitemaps.
Sitemap for Users: These sitemaps are for the users or the audience to help them in navigating from one tab to another without going in a hierarchy. They can directly go to the other landing page in just one click. These sitemap are visible on the website for user-view.
Sitemap for Search Engine Bots: These sitemaps are for the bots that crawl our website and update their database with new information that helps in increasing the number of URLs you have added in website or any kind of changes you made in URLs. These sitemaps are available for users and are uploaded in Google Webmaster tool. Google Bots crawl the website through their submitted sitemap and does it after a week, few weeks or even a month.
Now, looking towards the question: Will resubmitting the Sitemap effects the SEO current rankings?
The answer is No. IT will not hurt the current rankings of SEO. It should be updated as much it can be in order to get the updated changes you have made in the website. Submitting or resubmitting the sitemap will not cause any SEO rank drop. There are number of sites of web having dynamic sitemap that crawls on regular basis. There is one case to discuss i.e. if you are resubmitting the site, then there must be something updated. So, I will recommend to update your existing sitemap instead of resubmitting it.
The importance of Sitemaps should not be downplayed. They help search engines navigate your website more easily, which helps search engines index your content better. If you think of your website as a building, the sitemap is a blueprint that informs search engines exactly where everything is located. The sitemap of any website crawls periodically after a time interval and the sites having good PR get crawl more often than other with low PR.