Data Picks:
Many MYCADKEYS commands that require data input such as Layer names, Block names,Color, Linetype, Pline width that are available in existing objects can be supplied by clicking on a relevant object.
A left pick will supply the top level information and if relevant a right pick will supply the next lower level of information. For example If wishing to set a Layer to be current, a left pick of a Block will supply its insertion Layer whereas a right pick will supply the Layer of the object within the Block.
Doesn't sound like much but saves an enormous amount of time when responding to commands or researching the data.