As a rule you will only want to resubmit your Web site each time you update or change it and only if you are not ranking well. The search engines will not be instantly aware of the changes you made to your Web site. Therefore, you will generally want to tell the engine about your changed pages by re-submitting them. You can go to each search engine and individually submit each of your pages, or you can use WebPosition Gold's Submitter to create Missions to do it automatically. 

Unfortunately, there are pitfalls to submitting since each engine has their own set of rules and submission limits. Unlike many other submission products and services, WebPosition will try to warn you about known limits so you can avoid being penalized or having your submission ignored. If you try to submit too many pages at once, WebPosition will prompt you and suggest submitting only some of the URLs for that day. Surprisingly, the engines penalize for exceeding these limits but rarely ever warn the Webmaster if they exceed them. Also, resubmitting before the engine has had time to index your page is not necessary. After submitting, it will take anywhere from a couple of days to months for your submission to be integrated into their database (i.e., indexed), and for your ranking to change. The amount of time varies for each search engine. The WebPosition submission report generated after you submit will give you estimated times for each engine so you know what to expect. 

Regarding directories such as Yahoo, you will never need to resubmit unless the content of your Web site changes significantly or the description they chose for your listing is not accurate. The method to update or change your listing on a directory will vary. 

To order a copy of WebPosition Gold see: 

WebPosition internet marketing, search engine submission and web page ranking software