Once a site has been fully optimized, there is still a lot work still to be done. The first pass at keyword optimization isn’t always the best, making further edits necessary. After making the big, site-wide optimization edits to your site its often beneficial to go back and review things on a more granular level. You can find the areas that are up against more competition than others and explore further improvements that will be needed for even more improved success.
Unfortunately you can’t know how well your SEO’d title tags will perform until you make the edits, wait for the search engine to index the page, and check the results. Depending on how deep your site is and the frequency of the search spiders coming back, even the most basic changes can take several days to a week to show in the search results.
When dealing with ecommerce sites you don’t often get the luxury of making changes on a page by page level because everything is pulled from a database into templates. Generally it is counter productive to implement site-wide changes until you know how those changes will work. The last thing you want is for all your pages to drop in rankings at one time because you tweeked the global template for a new title or description.