Traders are better off NOT using documents like LOI, ICPO, FCO, etc. Even if and when they rarely are used in internal trades, on a restricted level within specific industries, they have no legal or customary basis in International Trade whatsoever. In fact the presence of many of these terms are considered to be signs of Advance Fee Fraud, by knowledgeable players and law enforcement.
There are various types of letters of intents for instance if you are applying for university or college then you would need to create a letter of intent for graduate school or university. If you are planning to apply for a job then you would need a letter of intent for a particular job position.