Explanation

To load balance with basic load balancer backend pool virtual machines has to be in a single availability set or virtual machine scale set.
A health probe is used to determine the health status of the instances in the backend pool. During load balancer creation, configure a health probe for the load balancer to use. This health probe will determine if an instance is healthy and can receive traffic.
A Load Balancer rule is used to define how incoming traffic is distributed to the all the instances within the Backend Pool. So if you delete the rule, load balancing won't happen.

Reference:
https://docs.microsoft.com/en-us/azure/load-balancer/skus