If you are an Exchange admin in a large organization where you have multiple domain in a forest and you just want to see all the Exchange object in the forest, you can use the following cmdlet
Set-AdServerSettings -ViewEntireForest $True
to change back, just change from $true to $false
Set-AdServerSettings -ViewEntireForest $false
In this mode, be careful when you ran any cmdlet as it will display all the related object in the environment if you are not careful with it. Eg. Get-Mailbox will list out all the mailbox in the forest. Imaging 20,000 mailboxes.
And to top it, Get-Mailbox -Database DBNAME | New-MoveRequest -TargetDatabase TARGETDBNAME. If you are not careful, you might move some other domain mailbox to yours. ahaha!