I've only ever blocked two people over the years, someone who managed to get hold of my number and bombarded me with random unsolicited messages, and another one who I'd met online Tinder who wouldn't take no for an answer.
However, from reading threads on here, some people block at the drop of a hat, with every contact or date that doesn't progress having to be actively "blocked", even if the contact/date has done nothing wrong. I don't understand why people can't just message and say "sorry, things aren't working out" but have to delete and block instead... it seems childish.