An example where -Unique is unique:
'a','a','a' | Select-Object -Unique
An example where -Unique is not unique:
Select-Object -InputObject 'a','a','a' -Unique
An example where -Unique is unique:
'a','a','a' | Select-Object -Unique
An example where -Unique is not unique:
Select-Object -InputObject 'a','a','a' -Unique