From GridLAB-D Wiki
The object_tree_balance global variable is used to control the use of automatic object index balancing routines. The --avlbalance command line option is used to control this feature.
Normally, the object index is automatically rebalanced to prevent low entropy lists from creating inefficient search trees when the object_tree_balance global variable is set to 1 or TRUE. When it is set to 0 or FALSE the tree balancing is disabled.