As far as SEO is concerned, Meta Tags have absolutely No importance. In the early days, Meta Tags used to have a lot of weightage, in the eyes of Google. But gradually, as with everything,people started abusing this technique, by stuffing keywords as their meta tags, for which they would like to Rank for. Google got smart, and so now gives zero importance to Meta Tags.

With regards to your next question, yeah, big websites, like Amazon and Ebay still have meta tags. This is not for the Seo purpose.

A title meta tag, is what a searcher will see, when his search results are displayed on his browser. If you search in Google, you'll find a short description, under the results displayed. These are Meta Tags. These are important, because a searcher clicks on a search result, after seeing this description. Most people try to include an interesting Meta Title with each of their post, so that They get more CTRs and so More Traffic.

For receiving great traffic you should have an interesting Meta Title, along with a keyword relevant Domain.Hope that Helps.

other search engines still use it but adding it isn't that much work and you never know

If you mean my "meta title tag" your page "Title" tag, the one that looks like this...

Then it has TONS to do with your seo.

I believe the previous posters might have thought you were referring to "meta tags" in general (description and keywords mainly) and in that case, they are of negligible worth.

But as indicated, the effort to maintain them, given automated tools for SEO, is minimal, so you should probably do it provided you have covered the more important bases of on-page SEO best practices.