An email can contain every relevant fact and still leave you wondering what to do. Imagine a community hall booking message with the room, date and price scattered through a long history. The information exists, but you have to assemble it.

Signal and noise is a useful analogy: signal is what helps this reader understand or act; noise is material that gets in the way. It is not a scientific measure of the quality of a sentence. A shorter message can be worse if it removes the date or an important condition.