请问:RtlSplay函数怎么样理解?

在源代码中它的英文描述如下:
The Splay function takes as input a pointer to a splay link in a tree and splays the tree.
Its function return value is a pointer to the root of the splayed tree.
在DDK中用图形描述如下:
[img]http://msdn2.microsoft.com/en-US/library/ms797584.treeRtlSplay(en-us,MSDN.10).gif[/img]
在ReactOS有一段英文解释:
    /*
     * Implementation Notes (http://en.wikipedia.org/wiki/Splay_tree):
     *
     * To do a splay, we carry out a sequence of rotations,
     * each of which moves the target node N closer to the root.
     *
     * Each particular step depends on only two factors:
     *  - Whether N is the left or right child of its parent node, P,
     *  - Whether P is the left or right child of its parent, G (for grandparent node).
     *
     * Thus, there are four cases:
     *  - Case 1: N is the left child of P and P is the left child of G.
     *            In this case we perform a double right rotation, so that
     *            P becomes N's right child, and G becomes P's right child.
     *
     *  - Case 2: N is the right child of P and P is the right child of G.
     *            In this case we perform a double left rotation, so that
     *            P becomes N's left child, and G becomes P's left child.
     *
     *  - Case 3: N is the left child of P and P is the right child of G.
     *            In this case we perform a rotation so that
     *            G becomes N's left child, and P becomes N's right child.
     *
     *  - Case 4: N is the right child of P and P is the left child of G.
     *            In this case we perform a rotation so that
     *            P becomes N's left child, and G becomes N's right child.
     *
     * Finally, if N doesn't have a grandparent node, we simply perform a
     * left or right rotation to move it to the root.
     *
     * By performing a splay on the node of interest after every operation,
     * we keep recently accessed nodes near the root and keep the tree
     * roughly balanced, so that we achieve the desired amortized time bounds.
     */

可我还是搞不懂它到底做什么的?还什么要这样做?
怎么理解它的逻辑,请大牛指点.