What are the effects of the Last Modifed Header (LMH) changing too often on a dynamic site?

Question

We have a web application that has a defect and is updating all pages Last Modified Header to the date of the last publish. We are in the process of fixing the defect, but we wanted to know if this defect might impact our SE results for this site.

Basically each time a page on the site get's updated all pages updates the last modified date even if the page has not been updated.

Is there any possibility of the Search Engine detecting the site as spam, since all pages are changing too often? -- Theory

Answer 1

It's unlikely to change much, since all the search engines will notice that your content hasn't actually changed. They will crawl at a rate commensurate with the observed rate of content change, more or less regardless of what you tell them, and small changes like that won't be marked as content changes in the index.

Answer 2

Changing the last modified date too often will NOT have a negative impact with the big 3.

The only way you can affect crawl rate via meta data (and sitemap.xml) is to reduce it. The reason for this is indicators that increase ranking/indexing are too easily abused. However, reducing spider rate is still an option for the resource conscious webmaster.