In the olden days I habitually ran defrags. Often several per day. Irrational because never got a noticeable performance gain. Embarrassing because I sat hypnotized and watched blocks being moved around for 3, 10, maybe 20+ minutes.
One of the first programs I ever bought with my own money was Diskeeper, to run on my DIY Windows 2000 tower. I could have used the built-in tool—which I later learned was based off Diskeeper—but its visualisations were even better. And like Jim, I was under the misguided notion that it made a huge difference in performance. Either way, SSDs saved us from so many things in our workstations and laptops, not least fragmentation!
These days, my most irrational action is to constantly close things not being used. Even if I know I’ll open them 20 minutes later. Better to close and re-open than to eat up a massive 3K’s worth of 5GB memory!
Also this! I see people’s macOS docks and Windows taskbars and I blanch. Even if I weren’t concerned about memory usage, I feel like cognitively there’s more overhead having too many things open to track. Right now on my Mac I have Firefox, Emacs, the Terminal, KeePassXC, our company’s self-hosted chat client, and Outlook; that’s it. My FreeBSD tower is about the same. And even that lists already feels like too much.
It’s a bit tricker now because awful, Electron-based software bundles entire web browser frameworks into applications that just deal with text. In that case, closing a simple program can have a breathtaking effect on resource use.