They help to build a system that is more robust across domains.
rather than trying to build a specialized system for every new target domain, as it has been done in most prior work on domain adaptation (Blitzer et al., 2007;Daumé, 2007), the domain adaptation problem boils down to finding a more robust system (Søgaard and Johannsen, 2012;Plank and Moschitti, 2013).