The first one of these exciting services, often overlooked, is clustering. Clustering provides a way to manage a scenario where you have too many markers. It provides a grouping technique for several markers to display as a single marker. This has many uses, one of which is to help you navigate quickly into the region you need to look at, without accidentally clicking on the wrong marker. That is a big one when you are working on a mobile device. Trying to click on just one marker in a sea of markers is difficult. You find yourself pinch zooming in awkward ways, trying to zoom in enough - to separate the markers enough - to get a clean click area. With the cluster, you will automatically be zoomed into the area by touching the cluster and can then drill down quickly to the single marker you seek.
The second of these services is a bit more common. It is the ability to add color to the markers. The ability to show all of your customers on a single map is great. When you are able to color-code them, you can truly explore your data. Having a different colored marker for varying sets of data becomes useful when you can adjust it easily. You might want to show the sales rep associated with a customer or mark the perspective value of customers in different colors. This is where refining the UI comes in to play even more.