Most people are probably using scrapers and crawlers to collect data on sites that either don't have an open API or the API is difficult to use.

Examples:

Ancestry.com scraper - https://github.com/mjhea0/ancestry-scraper

Indeed job scraper - https://github.com/mjhea0/indeed-scraper

Craigslist housing scraper - https://github.com/mjhea0/craigslist-housing-scraper

https://github.com/ThaWeatherman/scrapers

What can you then do with the data?

Monitor competition or your own brand

Sentiment Analysis

Gather sales leads

Machine learning

Generate content (blog posts, building a custom job board) Find cheap flights