The highest value for walnut trees (see below video) is making sure a nice long round log is harvested for pealing veneer.  The round log is spun and pealed down to a post.  This process is not possible with a split log. The best one can hope for with a split log is cutting some planks or firewood.  

Walnut, with its beautiful grain and rich chocolate color, is a prized wood for furniture and millwork. So a large walnut tree with a long, straight trunk can be worth $8,000 or more. However if the tree has heavy limbs in a Y-shaped crotch, it has to be felled with great care or the trunk might split in two, which drops its value to maybe $500. The lumberjack has to scale the tree up to the crotch and carefully cut off each limb as well as the remaining crotch. The goal is to leave a trunk looking like a telephone pole. Then a landing area for the trunk has to be carefully selected. It must be level and without obstructions. Otherwise the log might split and you end up with fancy firewood.

Long straight walnut logs are highly prized in the veneer industry. The log is spun on a massive lathe and peeled down to a post. A split log is useless for veneering.