Semantically, a meaningful class or id shouldn't always need to be qualified by the element type. There are certainly times when you'd want to, though, if the element type changes the meaning.
E.g., An e-commerce site that displays products in both the main content region and the sidebar. Product names use h1 tags in the main content region and h2 tags in the sidebar. Selectors like h1.product-title and h2.product-title have different meanings, and they're more efficient than the alternative selectors #main .product-title and #sidebar .product-title.
From a performance standpoint, qualifying class and id selectors by the element type is probably less efficient than not qualifying them, so doing it unnecessarily makes the selector longer and more difficult to maintain and decreases performance.
E.g., An e-commerce site that displays products in both the main content region and the sidebar. Product names use h1 tags in the main content region and h2 tags in the sidebar. Selectors like h1.product-title and h2.product-title have different meanings, and they're more efficient than the alternative selectors #main .product-title and #sidebar .product-title.
From a performance standpoint, qualifying class and id selectors by the element type is probably less efficient than not qualifying them, so doing it unnecessarily makes the selector longer and more difficult to maintain and decreases performance.