It's good to stay hygienic.
Bobby has been sweating all day at work, but he is so tired that he doesn't feel like doing anything but going to bed.
Bobby has to decide whether he wants to take a shower before bed.
Bobby decides that it is worth his last bit of energy to clean himself up before going to bed.
He decides that he's just too tired to take a shower tonight and slips into bed while he is still dirty and sweaty.
He emerges from his shower feeling fresh and clean, and he sleeps very comfortably for the whole night.
Bobby just can't get comfortable and sleep well, he doesn't feel clean and his skin is getting irritated by the bed linens against the dirt and sweat.