Hello there! I am a web developer and recently my boss asked me the following:
Since we submit an optimized site what is going on with spiders, and that is how often do they spiders pass from my site, do we have to resubmit the site to engines and directories, will the spiders pass forever and if that happens should i refresh the site's content?
Could anyone help me?

Submit it once. Google will decide for itself when it will crawl and how often.

I do however, suggest you submit a Google SiteMaps and keep that updated regularly.

Just keep making changes to the site and Google will keep coming back to check it out.

Since submitting a sitemap, I've noticed that my crawl rate has significantly increased and the amount of traffic google sends me has decreased / remained consistant. It could be other things I've changed at around the same time though :-/

no need to resubmit ever! to anywhere. If you have incoming links the crawlers will keep finding your site and if you have changed the content the results will reflect that after two or three days.