A computer-assisted system comprises a manipulator configured to support a tool, a lockable joint, and a controller. The manipulator extends distally from a base and comprises a distal portion. The lockable joint is coupled to the base and located proximally relative to the base. The controller is operably coupled to a powered joint. The powered joint is located distally relative to the base. The controller is configured to perform operations. The operations comprise: driving the powered joint to move the distal portion while the lockable joint is locked, and driving the powered joint to move the base while the lockable joint is unlocked and a position of the distal portion is externally maintained. A method includes processes for operating a computer-assisted system. A method includes determining a desired motion envelope for a tool supported by a manipulator, and positioning a base of the manipulator based on the desired motion envelope.