Scrapers are used, for example, to initially create web directories and keep them as up-to-date as possible. Scrapers are used to search parts of the Internet for relevant data and to copy what is found. The commercial use of scrapers in particular quickly raises legal questions, so that the use of scrapers is generally not unproblematic.
Further references:
https://de.wikipedia.org/wiki/Screen_Scraping
https://en.wikipedia.org/wiki/Web_scraping
The following video introduces the theory of web crawling, which has parallels to scraping:
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