If you have a dedicated bedroom that you don’t go into during the day, by all means: leave it any way you want. Or if you go to work right after breakfast and don’t get near it anyway. But if you tend to come across the unmade bed during the day, you might want to think about it.
An unmade bed is an open invitation. Even if you don’t actually lie down, chances are it had you thinking about it for a brief moment! If you’re easily distracted, that can put you right out of activity mode and into slacker mode. Or at least that’s my experience.
I inhabit one room that’s both bedroom and working area, and having the bed there means the transformation to working area will be incomplete all day. Also, it takes up a lot of space if I don’t fold it away (it’s a futon that I fold into a sofa), so the room will feel more cramped and untidy and messier than is good for my focus.
I even forced myself into the habit of putting it away before breakfast because back when I had breakfast first, I wouldn’t go on and make the bed right away. I’d lie down in it, maybe half make it, then get distracted by something that’s part of slack space and suddenly it was two hours later and I hadn’t started my day yet. (We also had a cat at the time. Without him, I’d probably have taken less. Not much ,though.)
I still like to lie down after breakfast and listen to some music until the coffee has run its course, but with the bed folded into a sofa, it’s just so much easier to get up off.