Once you have completed the majority of tasks you do not have to repeat them ever again (e.g. search engine submission). There are however a few tasks that are worth looking at regularly as they change on a regular basis. These task appear in their own section on the right hand side of the page and require you to revisit them from time to time to make sure your site is at its optimum level from a search engine optimisation perspective. A good example of this is Unindexed Pages - this will change over time as you add new pages and as the search engines find and index more of your site. It is therefore a good idea to check that any new pages you create are being indexed in a reasonable timeframe. Depending upon the size of your site this could be anywhere from a month to 6 months.