We have a saying in our firm that smooth transactions make successful transitions. Basically, if two parties cannot agree on the elements of the LOI, they will probably have a hard time negotiating while dealing with the minutiae of the purchase agreement. Normally, once the key points of the deal are negotiated up front, the rest of the transaction tends to work much more smoothly.
There is no filtering through legally written clauses and other such unnecessary information at this stage in the project. When the letter of intent spells out each detail clearly, the seller can come back with alternate terms of which he or she would be more accepting. This negotiation can go back and forth without the rewriting of lengthy pages that either party may misconstrue.