At its core, an LOI describes intent, and both parties are only legally bound to a few high level areas. These areas include: agreed-upon closing date, transaction expenses, full access to information, and confidentiality.
With that being said, once an LOI is understood and signed by both parties, an agreed-upon exclusivity period begins which allows the prospective buyer to perform their due diligence without having to compete directly with other buyers. This period can be extended past the set expiry date by the mutual agreement of both parties.