I thought this idea (of placing kumsa v'sudra - light objects) on the roof was very interesting. I had been struggling with the whole sugya - why would it assume that working with a place well below you (shilshul) is going to be easier than working with something above you (z'rikah)? I surely would find it easier to put things ten tefachim up, more than in a hole ten tefachim down! But here it is explained. As Rashi says, the usual usage of a chatzer is heavy things. It's got to be easier to lower a sofa (with ropes?) than lift it up.
It's only when we look at reshus harabim that we shift to saying that there people are doing light handling, like putting their handkerchief on something for a minute.
It's only when we look at reshus harabim that we shift to saying that there people are doing light handling, like putting their handkerchief on something for a minute.