Why I have a perpetual browser history
I've mentioned in passing that I keep my browser's history database basically forever, and I've also kind of mentioned that it drives me up the wall when web sites make visited links and unvisited links look the same. These two things are closely related.
Put simply, the visited versus unvisited distinction between links is a visible, visual representation of your current state of dealing with a (good) site. A visited link tells you 'yep, I've been there, no need to visit again'; an unvisited link tells you that you might want to go follow it. This representation of state is very important because otherwise we must fall back on our fallible, limited, and easily fooled human memories to try to keep track of what we've read and haven't read. This fallback is both error-prone and a cognitive load; mental effort you're spending to keep track of what you've read is mental effort you can't use on reading.
Of course this doesn't work on all sites (and doesn't work all the time even on 'good' sites). I'm sure you can come up with any number of sites and any number of ways that this breaks down, and so the visited versus unvisited state of a page is not important or useful information. But it works well enough on enough sites to be extremely useful in practice, at least for me.
And this is why I want my browser history to last forever. My browser history is the collected state representation of what I have and haven't read. It tracks things not just now, in my currently active browsing session as I work through something, but also back through time, because I don't necessarily forget things I've read long ago (but at the same time I don't necessarily remember them well enough to be absolutely confident that I've already read them). For that matter, I don't always get through big or deep sites in one go, so again the visited link history is a history of how far I've gotten in archives or reference articles or the like.
There is nothing else on the web that can give me this state recall, nothing else that serves to keep track of 'how far have I gotten' and 'have I already seen this'. The web without it is a much more spastic and hyperactive place. It's a relatively more hyperactive place if I only have a short-term state recall; I really do want mine to last basically forever.
(In fact for me anything without a read versus unread state indicator is an irritatingly spastic and hyperactive place. All sorts of things are vastly improved by having it, and lack of it causes me annoyance (and that example is on the web).)