With the rapid pace at which most of us browse the internet, it is easy to lose track of what we have already seen and where we saw it. There are some days when I'll look at 100 sites while at work, researching a particular topic, but less than 10% of them will be applicable. I have a rotten memory, so without some kind of reminder I would be doing the same search time and again. I use bookmarks all the time when I find a reliable, informative site that I might need again. Recently I've been working on a Civil War project at work and, as you can imagine, the internet is awash with Civil War websites. There are some go-to resources that I have been using for a while (I refer to the Wikipedia page on Union generals on an almost daily basis), but there are some much less obvious sources that I have come to rely on. I keep a folder in my internet browser devoted to the topic which I can refer to when I'm trying to remember which of the sites I found the week or month before that was so helpful.
I'm much less familiar with tagging, though I understand how it would be useful. I have so many bookmarks at this point (my desktop is littered with them) that it's easy to lose track of which ones were useful for which tasks. I use tags on my Instagram posts because they a) bring in more traffic for the images, and b) gives me a way to check what I've already posted. With over 400 posts I frequently don't remember whether I have already posted a book. Fortunately, since my earliest posts I have included the titles, authors, and years in tags. I've had some success in promoting my own weird tags: #greenpublishersbindingthursday is my greatest achievement because it's so cumbersome and specific, and yet it has 324 posts.