Why does Howard tell Willy to drop off his samples and forbid him to go to Boston?

Howard recognizes that something is wrong with Willy, and he wants him to go home and rest. He doesn't want a scene, but he's not going to allow Willy to work. Having him drop of his samples is pretty much the same as "you're fired." 

Oh, yeah. Whenever you can this week, stop by and drop off the samples. You’ll feel better, Willy, and then come back and we’ll talk. Pull yourself together, kid, there’s people outside.