This option is available along with the standard Targets feature and pursues the same objectives. It also could be found at the Targets tab of the Offer's Edit page and is enabled if you fill in the Alias field of the form:
Note: you can use Aliases only when the S2S tracking is chosen at the Tracking tab.
As soon as the target is added you can choose tracking without or with aliases:
The main value of using aliases lays in utilizing a single target's postback URL for all offers, where the target with the same keyword (alias) was added.