Deep linking refers to the technique of linking to an internal page of a website instead of linking to the home page of the website. This allows the users and search engines to directly land on the page of interest instead of coming to the home page of the website first and then browsing to the required web page. HTTP does not actually discriminate between “deep” links and any other links but many websites prefer their visitors to enter directly on pages they’re most interested in so that better usability would satisfy user’s needs and the current, specific interest of the visitors could increase their sales.
You should not prevent deep linking because it takes users to their preferred destinations as quickly as possible. It also ensures that the spiders will crawl deeper into your site thus increasing the chances of your website ranking higher on the SERPs. If you avoid deep linking, you would not convert many visitors arriving from search engines into potential customers.
Deep linking is also important for improving your website rankings on the search engines. The landing page which is linked directly achieves improved visibility on the search engines due to the links it receives from other websites and web pages.