The use of disk shares will work just fine as long as the datastore is seen by a single ESXi host. Unfortunately, that is not a common case. Datastores are often shared among multiple ESXi hosts. When datastores are shared, you bring in more than one local host scheduler into the process of balancing the I/O among the virtual machines. However, these lost host schedules cannot talk to each other and their visibility is limited to the ESXi hosts they are running on. This easily contributes to a serious problem called the noisy neighbor situation:

The job of SIOC is to enable some form of communication between local host schedulers so that I/O can be balanced between virtual machines running on separate hosts. We will learn more about how SIOC functions in the How it works... section of this recipe. Before that, we will learn how to enable SIOC.