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I routinely delete those codes with absolutely no negative effects that I can see. As far as I know, this just means that the defaults kick in, and that's what I want anyway.
In the future, with more of the world online and more uses for the internet in place, these tags may become "vital", as you say.
However, I also don't think there is a lot of gain to be had by deleting them. The HEAD section looks a little cleaner but download time is only improved a mere smidgen.
IMHO some search engines use
<META HTTP-EQUIV="content-type" CONTENT="text/html;charset=x-xxxx">
to determine the language and character set of web pages.
I agree that there are probably no negative affects in deleting the tags, however there appears to be an advantage in their use for multilingual sites.
For every English page on my site I provided a link to the corresponding Japanese page. In all the Japanese pages I used
<META HTTP-EQUIV="content-type" CONTENT="text/html;charset=x-sjis">
It appears to have benefited in relation to Japanese pages being indexed with search.msn.co.jp, Google and Fast.
Although I never submitted Japanese pages to any of these search engines, I have several high ranking and number one ranked pages with all of them.
Google and Fast have been spidering my Japanese pages for about a year.
I have come to the conclusion that these Search Engines indexed my Japanese pages when they first started building their Japanese databases.
Here's a link [w3.org] to an ftp download of all the registered charset values. I'm sure that sooner or later I'm going to need some of this info.
There's links to lots of other helpful references on this W3C page as well.