I just came across the question How to override product search result block and my immediate reaction was "this has to be a duplicate".
But any question I found about the topic was something along the lines of "I tried to rewrite this particular block, this is my config, why doesn't it work" and depending on which mistake has been made the answers are different. None of these are a good fit for a canonical question, even if the question is edited to be more general.
In short, I'm looking for a question like this How to Override Core Block, Model and controller in Magento2 for Magento 1 - is there already something on StackExchange?
If not, I am willing to write one with added bounty to answer all these questions one and for all.
I am aware of the famous inchoo blog post but cannot close questions as duplicate for that :)