Why do you need this feature in your server? Mostly all new web servers support this feature and you are mostly not needed to worry about it, cause you have to worry about it when your site have thousands of pages, posts or links which google bot or other search engine bots have to crawl. And they can use huge bandwidth of your server and CPU usage of your server to respond them for all pages.
Bots of search engines spider almost all sites every day so to not waste google or other search engine bot’s resources and your resources, and increasing your hosting cost is better for both you and search engines.
This feature in server just tell the spider from search engine that which page was last modified, which is same when they last visited, which have done some changes after their visit, and which pages was added new, means all stat about website changes and what is consistent since they visited before. Using this information bots do not crawl all pages including old as well. Cause that waste spider’s time and your bandwidth as well which can result in cost about your web server.
Again you don’t need to worry about if modified since HTTP header unless you have thousands of pages in your website. Cause this feature is important now a days so almost all web servers have this feature in their server. For more information please contact us. Thank you.