The scope. Internal stud wall framing, including the coordination required to get insulation in ahead of lining.
Internal framing is a services problem. Internal walls carry plumbing, electrical and sometimes mechanical. Frame them without allowing for the services runs and the plumber cuts them out later, which turns a structural wall into a compromised one. Coordination before framing is cheaper than remediation after.
Setting up the linings. A lining contractor can only be as good as the frame behind them. Studs at consistent centres, plumb and in plane, is the difference between flat walls and a plasterer chasing packers across a whole floor.