It takes longer to write cleanly and crisply.  It shows respect for the time of others when you do.

Learn to type with your thumbs on a BlackBerry-like device.  That will really discipline you to use shorter sentences and shorter words.

As you grow in position and assume roles of increasing responsibility and complexity, you truly appreciate those who communicate with brevity and clarity.  Their emails, notes and reports will get read!  Conversely, and sadly, good ideas in hard-to-open packages wrapped with complicated bows may be overlooked.