It's all about branching factor. Because of the way B+-Trees store records (called "satellite information") at the leaf level of the tree, they maximize the branching factor of the internal nodes. High branching factor allows for a tree of lower height. Lower tree height allows for less disk I/O. Less disk I/O theoretically means better performance

In a B- tree you can store both keys and data in the internal/leaf nodes. But in a B+ tree you have to store the data in the leaf nodes only.

A B+ - Tree is in the form of a balanced tree in which every path from the root of the tree to a leaf of the tree is the same length.

Each nonleaf node in the tree has between [n/2] and n children, where n is fixed.

B+ - Trees are good for searches, but cause some overhead issues in wasted space.