Related to removing impediments is the skill of identifying root causes, typically called Root Cause Analysis (RCA) within the technical world. Some Project Leaders (be it a traditional Project Manager, Scrum Master or something in between) may believe that RCA is really a skill that the team has full ownership and that the Scrum Master should simply connect people with the right resources to either swarm or focus on the right path to resolution, but believe that approach is short sighted.
An experienced Project Leader will be like the Larry King of root cause investigation, asking questions to determine the signs of where a root cause may be found. Project Leaders should help “connect the dots” like Steve Jobs has been famous for saying in his Stanford Commencement address in 2005 (http://news.stanford.edu/news/2005/june15/jobs-061505.html). Connecting the dots isn’t just about product vision or strategy but finding the missing part that is blocking the team from completing the blocked task.
Confident many reading this are already thinking along these lines, so I’ll state that there are times with the Project Lead will have no clue about the root cause and should instead play the role of observer so they gain more experience on helping identify trends for future issue resolution and impediment removal.