Hi,
imho there is no real advantage: the ESXi installation uses just a few GB (its installs in some reserved partitions that use about 8 GB) and when fully booted the whole hypervisor will run in memory using the disk only for logs. Keep in mind that only its reserved partition are used for logging.
So there is no real issue about performance.
Talking about reliability: if you are using the server in a production environment for me is a no brain: go for a raid 1 configuration. You will have better reliability and better performance (in raid 1 all data are mirrored between the 2 disks and all reads come from the 2 spindles).
If it's a lab/training server just figure out if you need the extra space or not: the trade-off is between performance (raid 1) and space (one raid 0 or 2 disks with no raid). Another option is to install ESXi on a USB key: you can use a 4 GB usb key.
HTH
