Understanding it
Google’s guide on the topic is aimed at sites with over a million pages changing weekly, or over 10,000 pages changing daily. A brochure site with a few hundred pages need not worry about it.
On a large site, budget is wasted on useless pages: endless search filters, duplicates, URL parameters, redirect chains. Important pages then get visited less often.
The levers: block crawling of worthless areas, remove duplicates, respond fast and keep the sitemap up to date.
A concrete example
Illustrative example: a listings site
A property listings site has hundreds of thousands of URLs, mostly filter combinations. New listings take days to appear in Google.
Crawling of filters is blocked in robots.txt and the sitemap only lists active listings. New listings get crawled faster.
The common mistake
Worrying about it on a small site
Optimising crawl budget on a 50-page site changes nothing: Google crawls it with ease. On a small site, work on content and links, not crawling.