Update design guidance to not block health probe w/ NSG rules

Author: thisisanniefang

articles/load-balancer/load-balancer-custom-probe-overview.md

@@ -100,7 +100,9 @@ For HTTP/S probes, if the configured interval is longer than the above timeout p
 
 * To test a health probe failure or mark down an individual instance, use a [network security group](../virtual-network/network-security-groups-overview.md) to explicitly block the health probe. Create an NSG rule to block the destination port or [source IP](#probe-source-ip-address) to simulate the failure of a probe.
 
-* Unlike load balancing rules, inbound NAT rules do not need a health probe attached to it. 
+* Unlike load balancing rules, inbound NAT rules do not need a health probe attached to it.
+
+* It is not recommended to block the Azure Load Balancer health probe IP or port with NSG rules. Doing so can result in the health probes being unable to determine the accurate health of your backend instances.
 
 ## Monitoring