Just wondering, i have been looking at a few SEO programs and websites and major search engines, and it seems a lot of them offer to resubmit your website to major search engine every month or every few months. Does this affect your ranking? if not why are SEO companies charge a fee for it and offer this service?
I always though once you submitted your website its index on the website forever. please correct me if I’m wrong.

I think resubmitting might make your website look like spamming.

any thoughts?