how often should I generate sitemaps ?

I update my web site everyday.

I want to know

1. how often should I generate sitemaps ?
2. Is there a way to check if google sitemap really helps my site in SEO or not.
3. besides help google spider to search my site quicker, whatelse does sitemap do ?

 

if you generate a lot of new content daily, i'd update the sitemap and ping google daily, can't hurt.

 

1) Update your sitemaps when you add new content to your site.

2) Define 'help'. SEO is the combination of hundreds of factors and little details. Sitemaps help, no doubt about that. Getting rank requires more than 'just sitemaps', but sitemaps are one of the many pieces to helping get rank as quickly as possible.

3) The Google XML file helps Google to find your pages quickly, but mostly it helps them to spider your site more efficiently. Using the Google sitemap, they can tell roughly how long between when your pages are updated and how long it's been since they were last updated. Of course you can lie to them and say that every page is updated daily and they were all just updated 'now', but this doesn't help anyone (you or Google).

I have several sites that are getting spidered on a very infrequent basis, but they rank well in the search results.

This is the same logic behind If-Modified-Since and Last-modified headers which may need to be added to your pages. The HTTP Header Checker at AutoMapIt will show you if you are using those headers for your pages or not.

If you are using them, Google can simply check to see if their last version of your page has changed since they last visited that URL. If it's changed... they crawl it and process it.... if it hasn't changed, they'll look for a different page to crawl.

Saves bandwidth, saves time, Google's happy because your site doesn't slow down their spiders or page processing time (they can cover more ground) and they really wouldn't have gotten anything new out of your page anyway.

 

Updating the sitemap everyday could be time consuming.
I would say about once every week.