I think it is courteous to learn something about the company but what irritates me are the companies with "mantras" that are often displayed on the reception area wall. I once attended an interview with a well-known supermarket company for an admin role so had a look at their website to understand the company values, which can be different from what you actually witness as a customer.
Wasn't asked anything about company values but had to demonstrate how I would deal with different situations and if there was anything in the past where I learned from a mistake, either committed or averted. They assumed, rightly or wrongly, that I knew their company but they had also taken the time to read my CV and ask sensible questions. Unlike an interview many years ago, where I was asked some ridiculous questions such as if I died tomorrow, what would I like inscribed on my headstone. I resisted the temptation to reply "I don't care as I won't be able to see it".