As a reader I DO NOT give kudos just because I managed to finish something. It’s not a “good job, you meet my minimum requirements”. I give kudos because I liked it, and I know that other readers (especially those new to the fandom) often sort fics by how many kudos it has, and I want to add to that number to give it a good reputation. If you get a kudos from me it means that I think other people should read the fic too. And if I really really loved it I’ll add it to my bookmarks too.
As a writer I fucking love seeing the kudos go up on my fics. Since hits are skewed by chapters, age of the fic, serial posting vs finished posting, etc, I don’t pay attention to them. But kudos give me an accurate number of how many people liked my fic. Comments are lovely because they give a personal message, and on a small scale give me an idea that someone enjoyed my fic. But I can look at my kudos and be blown away by the sheer number.
That many people liked my fic?? Holy. Shit.
I’m lucky to have very verbal readers who leave lots of comments. I have seen authors I adore get less feedback, so I know just how lucky I am. But those kudos also mean the world to me.
I love comments, but if all you’ve got the spoons to do is click the kudos button, you can trust that I notice and appreciate them :)