clustering provide hierarchical topology support in routing protocol instead of flat topology. In cluster based routing protocol the cluster head coordinates all the routing activity. So cluster node  have to maintained only topology information instead of all the node in flat topology . so in this way clustering reduce the control overhead for route formation and maintenance.

The role of cluster head should be regularly rotated among the nodes in a cluster (say, based on the residual energy); this way, cluster-based routing can be both energy-efficient and scalable. With node mobility, it is better to prefer nodes with higher residual energy and lower mobility as clusterheads.

Clustering is available as both data mining technique and machine learning technique. Choice depends on, what you want to achieve using clustering?

You can have look at this book : 

Data Mining: Practical Machine Learning. Tools and Techniques, Second Edition. Ian H. Witten and Eibe Frank.

The e-book is available on the web.