The stealth-focused chapter trait is unique to the Raven Guard as the siege warfare specialists one is to the IF. As siege warfare can be represented in a lot of different ways so does stealth. But if your question were "what is massive use of stealth good for?" then I would have answered: ambush expertise, infiltration expertise, sabotage expertise, assassination expertise... In brief, all we need for some good guerilla warfare; with the main idea behind that if you strike the legs (sabotage) or the head (assassination) first, then taking the rest of the body down shouldn't be too much of a task, having the initiative is important as well. The Raven Guard also use a lot of jumppack equipped assault marines, with an unusual number of lightning claws. These troups are not necessarily better than other assault marines, but in the case of the Ravens they are unusually numerous. The sons of Corax would also choose fast attack vehicles such as Land Speeders and Bikes over more heavy ones, like Predators and Land Raiders. Overall, the Raven Guard is stealth-focused infantry-heavy (=/= heavy infantry) chapter adept of guerilla warfare. They can in this respect be (to some extend) compared to real world modern armies and special forces units.