In my case, having something to keep me busy makes time move along faster so I'd rather have constant work than downtime so it feels like I am getting done with work and going home faster.
Reading/using my phone does the opposite. 30 minutes feels like 2 hours. I want 2 hours to feel like 30 minutes. Factory and routines that never end don't work this way, though. But stocking shelves or cleaning toilets does; I think it's because I can actually see that I have accomplished something, unlike when you do 1/100th of building the same exact thing for 8-10 straight hours and don't even necessarily see the end result.