A LOI is typically used as a "starting place" for negotiations on a property. Generally a LOI will be followed up by a formal Purchase Agreement after the terms are settled on. This may or may not be the case in your area, but is a good use of the two documents.
When "LOI" is used, it actually refers to the Letter of Indemnity. This is standard usage of the term and has been for decades. The Letter of Intent (hereafter referred to as LOI) is often used in specific domestic trades, such as in real estate or corporate mergers, but it has no standard usage in International Trade itself.