If the desired cache to capacity ratio is very high, it may require multiple flash devices per host. In this case, multiple disk groups must be created to accommodate this since there is a limit of one flash device per disk group. There are significant performance advantages to using multiple disk groups. They typically provide more IOPS and also reduce the failure domains within a host.
The more cache capacity, then the more cache is available to virtual machines for accelerated performance. However, this leads to additional costs.
Design decision : For all but the lowest performance needs, start with two disk groups.