Most business envelopes have their logo and business address pre-printed on the envelope, but if you are in a large organization with many people sending letters out every day, how will your Mailroom staff know who to give the envelope to if it comes back Return to Sender? A good tip is to put your boss's initials under the logo and address on the envelope. Then if the envelope is returned your Mailroom will know who sent it and can return it to the proper person. This is especially helpful when you are doing a large mailout as there is usually some mail returned.
Another reason to put the author's initials on the envelope is if the Mailroom staff notice your envelope is missing part of the address or name. With the initials on it they will know who the author is and can return it to be corrected.