It all depends on the purpose of the LOI, remuneration, contract length and key details of the contract are sometimes included. Sometimes the LOI is used instead of a contract when "yeah we want to contract with each other but only when we know that X,y & z have happened", i.e. conditions precedent, if any of those are not me it falls apart and is no longer binding. If they are all met it may well be binding. Penalties can be included on a party who backs out other than through the conditions not being met. Sometimes there is none of that and it;s just a group hug letter that says "we like each other and maybe we'll work together but only if we agree everything in a separate document (i.e. a contract later on, maybe)".
I think we'd all need need to see the instrument in question to see how binding it is, or if it's a group hugger. From my experience could be anywhere between the two extremes.