It is quite tough to indicate search engines to crawl pages or not to crawl pages. It is often happen with small and large websites. There are certain reasons like if you have removed old page from your website or moved old page to new page or you have updated your page content and in many other way.
If you are in the process of cleaning up your website and want to remove outdated pages or unwanted pages from your website. It is advisable to return 404 Page Not Found error if you have removed page from your website this tell search engine the particular page you are looking for is no longer exist on the website. Do not print simple 404 Page Not Found error code for your outdated web page, make your 404 page user friendly through your hosting control panel. Most of all web hosting companies offer customize 404 page.
If you have changed your existing page that you think your user might be looking for then you can use 301 and 302 response code to let search engine know your page moved to the new destination and your user will redirect to the new page. If you are re-organize your website its better to use 301 redirect to let search engine know that you move permanently to the new location.
302 redirect is useful in case when you have website that frequently update and the user can find their older post somewhere else on your website.
Your website is a static website and you have not updated your website from long time then you can tell search engine not crawl page again to avoid usage of extra bandwidth and http request. You can send ‘304 Not Modified’ through HTTP header to tell search engine that this page is not modified.