Hello sel57,
By default ESXi checks the storage type and then depending on the storage type it sets the default policy best suitable for that storage type. For details you can check the following:
Chapter 23 : Understanding Multipathing and Failover
Also you can check at the HCL link. For each storage vendor, type, Firmware version and ESXi version there is a suggested Path Selection Policy. So depending on the storage vendor, type, Firmware version and esxi version the best path selection policy is selected by default.
VMware Compatibility Guide: Storage/SAN Search
For example, in the above link I searched for EMC and ESXi 5.5 U1.
So in short the default is set and tested one and at time of booting the best suitable policy is selected. If there is any specific reason or suggestion from storage vendor then only you should change the default policy otherwise not.
Hope this answers the question.