Why are some pages indexed but not cached by Google?

[mRELEVANCE]

The question is simple but I don't understand the answer.

I found a webpage that was linking to my personal site. The page was indexed in Google. However, there was no cache option and I received a 404 from Google when I tried using cache:www.thewebpage.com/link/.

What exactly does this mean? Also, does it have any negative implication on the SEO value of the link that points to my personal website?

[john4math]

If you stick the following meta tag in the of a page, Google and Bing won't show cached versions that page on search results pages:

It shouldn't have any impact on SEO.  It only means that archived versions of pages won't appear be provided by the search engines on search result pages.

As far as reasons to do this, we use it on pages of our site where the cached page would be blank, because the page contents are loaded by AJAX, and the cached versions wouldn't load that content.