It's a wonderful and very flexible system well worth using. Many users like to personalise their letters with a unique signature. This can range from the short Bye to lengthy quotes filling up half a page. There are no rules you have to follow. I would suggest though that you don't overdo the length of your signature.
Some people have the ability, accidentally or intentionally, to annoy other users on the Internet.
Multiple postings, blatant adverts in the wrong place, and making offensive remarks in sensitive newsgroups can lead to reprisals. You may well get mail bombed. The idea behind mail bombing is to fill the target's mail box with so many rubbish messages that it takes them ages to download it and clear it from their system. This is sometimes used to let advertisers know that you don't want their unsolicited mail. I am not going to say that Mail bombing is a good idea.