To add to the responses, this issue is not related to the version of ESXi. The reason it's best to disconnect from the SAN while installing ESXi locally is that during the install, the installer will scan for storage devices and return everything it sees. This includes local disks and LUNs on storage array. If you're not careful, you could accidentally install ESXi to a LUN on the storage array and overwrite the existing data on that LUN. This is usually very bad. To avoid this simple mistake, when installing ESXi onto local storage, simply disconnect the server from the storage network or unmask any LUNs associated with that server to minimize the opportunity to make this mistake.
Cheers,
Mike