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The only time you need to use a robots meta tag is to exclude robots from indexing or following links on a page. If you want everything to be indexed and followed, you don't need it at all.
In terms of SEO, the description meta tag can be useful as it is sometimes used as the snippet under the URL in the results, but that's all. There are no other meta tags which have any effect whatsoever on how often your site will be crawled. For good results, you need good on-page content and especially lots of inbound links.