I always highly suggest extended axis. Avoid Group 2 if you can.
- DCS is a nightmare if your rail is setup for group 2. Fencelines/operator spaces move with the robot.
- Any type of frame shifting/ work in cartesian space is a nightmare because the robot doesn't know its moving when the RTU is moved.
- If you have to reposition your RTU, you have to reposition your robot as well. With extended axis, you have (World 'S' G1) motion type which will keep your TCP in the same point in space while you jog your rail axis, and move group 1 to account for the rail motion.