add examples for interpod configurations

docs/concepts/configuration/assign-pod-node.md

@@ -120,7 +120,7 @@ zone XYZ, but if it's not possible, then allow some to run elsewhere".
 
 Node affinity is specified as field `nodeAffinity` of field `affinity` in the PodSpec.
 
-Here's an example of a pod that uses node affinity:
+#### An example of a pod that uses node affinity:
 
 {% include code.html language="yaml" file="pod-with-node-affinity.yaml" ghlink="/docs/concepts/configuration/pod-with-node-affinity.yaml" %}
 
@@ -139,6 +139,31 @@ If you specify multiple `nodeSelectorTerms` associated with `nodeAffinity` types
 
 If you specify multiple `matchExpressions` associated with `nodeSelectorTerms`, then the pod can be scheduled onto a node **only if all** `matchExpressions` can be satisfied.
 
+#### More Practical Usage
+
+Than directly using with pods Interpod Affinity and AnitAffinity will be more useful when they are used with higher
+level objects such as Statefulset, Deployments, etc.  One can easily configure and prefer if two workloads should
+always be co-located in the same node or never be co-located in the same node.
+
+##### Always co-located in the same node
+
+A web application has an in-memory cache such as redis, one may prefer to co-locate their web server along with the cache as much as possible so that they have minimum latency like below.
+
+|       node-1         |       node-2        |       node-3       |
+|:--------------------:|:-------------------:|:------------------:|
+| *webserver-1*        | *webserver-2*       | *webserver-3*      |
+|  *cache-1*           |   *cache-2*         |   *cache-3*        |
+
+##### Never co-located in the same node
+
+Highly Available database statefulset has one master and three replicas, one may prefer none of the database instances to be co-located in the same node.
+
+|       node-1         |       node-2        |       node-3       |       node-4       |
+|:--------------------:|:-------------------:|:------------------:|:------------------:|
+| *DB-MASTER*          | *DB-REPLICA-1*      | *DB-REPLICA-2*     | *DB-REPLICA-3*     |
+
+[Here](https://kubernetes.io/docs/tutorials/stateful-application/zookeeper/#tolerating-node-failure) is an example of zookeper statefulset configued with anti-affinity for high availablity.
+
 For more information on node affinity, see the design doc
 [here](https://git.k8s.io/community/contributors/design-proposals/nodeaffinity.md).