This is very useful especially when you work on table or for kitchen garbage. You can leave one beside your hand, and toss any tiny trash into it.
You can make one with newspaper or useless flyers.
Of course, you can throw your trash into the trash bin directly. I am afraid that it sounds like a crazy idea, but I do not want to besmear or soil my trash bin with trash. ( Again, I know I am crazy.) I think most Japanese does not like to throw wet trash directly into trash bin. Japanese prefer to protect the trash bin with plastic bag that we get from supermarket for free so that the trash bin is always clean. Additionally, person like me prepares a paper trash box so that no wet stuff or tiny dust will not dripped or dropped from the plastic bag covered on the trash bin. It is such a paranoid to make a trash box in order to keep trash bin clean !
I admit that.