I've found that for me, spreading things out and having visual cues allows my brain to relax and focus on the task at hand, because I know I don't have to use a memory slot to remember to do something that I don't have a visual cue for, because every so often I see that cue and know it isn't going anywhere until I have time to deal with it. Almost the exact opposite of the anxiety the author describes. (And before it's suggested, yes, I also take notes and put important tasks there, but it isn't as helpful for my brain to let something go compared to having a visual cue.)
I work better with a conceptual (but not actual) blank slate, by asking myself each day what the top three things are that I need to get done that day, and not allowing an ever-growing TODO list to get in the way of seeing what's important.
It happens because I will have ctrl+c'd something several minutes ago. My mind subconsciously "holds" onto the info that I have text copied in my clipboard. It's only when I ctrl+v it and consciously discard it does the nagging go away.
I have no idea why it happens or if others experience this too. But I fully agree with the author about starting from nothing and getting rid of the clutter you think isn't bother you but which you're probably subconsciously holding onto.
That said, copying and pasting (and the attendant switching between windows/tabs) does often feel like one of the biggest cognitive frictions I have to deal with in any given day. That's a nut I'd like to crack one day.
One thing that has helped me the most in that regard is Alfred's multi-clipboard feature, where I can append to clipboard, which means I can copy-paste N links in N+1 actions instead of N*2 actions.