Why it is needed
The bot visits the website on its own schedule, and a new page might wait weeks to be crawled. A recrawl request moves it up in the queue, so the page gets indexed sooner and starts generating traffic earlier.
What this means in practice
With regular publishing, recrawling becomes part of the process: you publish an article or term – and immediately submit the URL to both webmaster tools. Request limits are capped, so specific important URLs are submitted rather than the entire website at once.
What recrawling does not do
It does not guarantee indexing and does not affect rankings. If a page is weak, blocked from indexing, or duplicates an existing one, an expedited crawl will only reveal this to search engines faster. Also, recrawling is not needed for pages with a configured redirect.