Some people nowadays might think that with technology increasingly being used to communicate, for instance texting and tweeting, there is less use for punctuation. Perhaps so in the media I have just mentioned, but in formal communications such as letters, CVs, reports and books, it still serves an invaluable purpose: to enhance clarity and avoid misunderstanding and ambiguity. Take the comma, probably the most used punctuation mark after the full stop, and consider what it does to the meaning of the following sentences.
1. The teacher said that the man was an idiot.
2. The teacher, said the man, was an idiot.
The use of the commas completely changes the meaning of the sentence and who is indeed the idiot!
Of course, that is not the only use for the comma; it is used to separate items in a list, to separate clauses, and to mark off parentheses and direct speech, to name but a few.