It also insures that the submission process completes properly and if not, the site is scheduled for re-submission. One reason we submit to the hundreds of link sites is because of the trend among the major engines toward counting link popularity as part of their own ranking algorithms. The theory being that the more a site is referenced elsewhere on the web, the more important it must be. Suggest an appropriate category and sub-category for those sites that require it. Submitting your site to an engine does not guarantee that it will be listed.
Sites can and do drop out of engines over time.
Search sites vary wildly as to how long it takes to list a client site. Some take months to list the site, while others index the submission instantly. Generally optimal results are realized 4-6 weeks after submission and begin to erode over time.