Your answer explained why it is helpful to google. It does not explain why individuals post "me too," or why people are posting "me too" here on the HN page...
There is a similar behavior here on HN with nice- page / I-agree / congrats posts. I'm wary of a general guideline that I should only post to HN if I think the karma reward will be greater than X, but more often than not I think it helps make sure any of my posts actually increase the numerator in the SNRatio.
Since the per post karma have been removed the only way to show you agree is to write an "I agree" post. If I upvote it only the author will see that someone upvoted it, but it is also information that is valuable to others. Hence, the only way to truly support a comment is to write a "me too" or try to rewrite "me too" into some rambling as if you had something else to contribute with but don't (which is arguably even worse).
Not defending it or saying that hiding the per post karma is bad, but it is understandable and one of the drawbacks of hiding the per post karma.
"Me too" is often used as a way to bump a forum thread back to the front page of forum software so that mods and others can have time to participate before the thread rolls off into murky ancient history. For instance, you very often see this in game forums.
Now, my pet theory is that game forums seeded this behavior, and now more people use it even on forums where it is technically unnecessary.
That said, I wonder what the game theoretical explanation is.
There is a similar behavior here on HN with nice- page / I-agree / congrats posts. I'm wary of a general guideline that I should only post to HN if I think the karma reward will be greater than X, but more often than not I think it helps make sure any of my posts actually increase the numerator in the SNRatio.