Netiquette or Internet etiquette is important because online communication is typically non-verbal. This means that it is very easy to misinterpret what somebody else is saying.
It is therefore useful, especially in cross-cultural or professional communications, to adhere to a mutually understood code of communication and etiquette. For example, typing in capitals is considered to be shouting, while all lowercase can be difficult to read. Proper capitalization is advisable in business or formal contexts, at the very least.
Furthermore, jokes and sarcasm without the normal usual visual cues of facial expressions may be interpreted as criticism or hostility. To avoid misunderstandings of this sort, emoticons, such as :-), ;-) or :-p might be used.