"Send this E-mail to five of your friends for good luck."
Why should you avoid forwarding this type of mail? If you send an E-mail to five of your friends, and each send it to five of theirs, eleven friends down the line you have close to fifty million chain E-mail letters bouncing around the internet. With all of this junk E-mail going around and growing exponentially, Internet service providers may have to invest in faster equipment or more phone lines. Who pays for upgrades? You and I pay through higher rates. Also, after receiving your tenth lucky tweety bird, the message tends to get annoying.
"This E-mail is being tracked by so and so... you too could be a winner after you pass this E-mail on to fifty people."
Actually there is no tracking going on, the intent is to get the most messages sent.
I believe that some chain E-mail is used to harass a certain individual. Their name and contact information is given, maybe even a home phone number. Again, this type of E-mail has the potential to grow exponentially. Also, it gives the intended victim a bad name as the originator of the message when no prize is rewarded or the information provided turns out to be false.