Search Engine Submission - is a process web pages owner to submit their pages to search engine in order get indexed on it and webmasters usually see this process as way to promoting their web pages, Normally it not necessary to do that because all major Search Engine like Google Search, Bing, Yahoo, AOL, etc use their bots (crawler or spiders) to find web pages from The Internet and index them to their database. So there only 2 reasons why webmasters keep do a submission to the search engine:
Because most peoples start to use search engines to find information that why most web pages want to be listed on Search engines so they find the way to do that. There 2 methods used by webmasters until now, They can submit their homepage site into search engines and leave the rest to bots index their entire pages inside, Or they can generate XML sitemaps that contain all URL of their website. And because most search engine users not like to look over than one-page results (SERPs), webmasters High eager to get the position in Top 10 in a search engine results.
To obtain a good position in search engines they struggle to optimize their web pages and this process called as Search Engine Optimization (SEO), SEO covers many aspects like keywords density, web pages structure, web pages Loading Speed, Meta tags, Links Popularity, Page Rank and much more.
Unlike the Major Search Engine which possessed with ability auto detect and discover new web pages by sending bots to crawling them, many small search engine like Baidu.com in China is most popular while Google in second place. Without Submission services to these search engines, your web pages may miss millions of visitors who might come from this Baidu.com.