I think the important thing is that every piece of space must have a specific and memorized use. For example, you may have an Outbox tray on your desk for outgoing mail and for stuff you need to take with you the next time you leave home/office, or a For Filing tray, but you may choose to keep that stuff in labelled files in a drawer or beside the filing cabinet or on a table beside the door, if you prefer to retain more desk space. It doesn't matter where you put your "To be Done Doday" stuff, as long as you have a reminder in your Calendar and you know where the materials are. The important thing is to do it today. Once it's done, where you kept the materials temporarily becomes irrelevant.