connect exchange server from remote machine failed with error

hi,

Try  to connect exchange server from remote machine.

$session = new-pssession -connectionURI "http://XXXXXXX/powershell?serializationLevel=Full" -ConfigurationName "http://schemas.microsoft.com/powershell/Microsoft.Exchange" -Credential $user

Import-PSSession $Session

failed with access denied error 

then   i checked the remote machine , to know how trusted hosts configured .

machine confgured with 'trustedhosts *'

then i reset trusted host settings to null value.. its works fine

my question is ,what is the difference between 

Set-Item wsman:\localhost\client\trustedhosts *

and

Set-Item wsman:\localhost\client\trustedhosts null

thank you

sumith