Hi @tbh,
tcp related question:
tcp rot and lin provide information on the current path travel and state.
Imagine that you develop an application that uses a robot for glue deposition on some path. If you know the speed at which the nozzle (tcp) is advancing in the current path domain [tcp_lin, tcp_rot] and the required volume of glue per unit linear distance on the path, you can control the actuator that presses the syringe with the glue to deposit the correct amount of glue.
Side note:
tcp_lin and tcp_rot are experimental features. If you wish to send low-level joint trajectories to ros_controller, we support skipping tcp_lin and tcp_rot, you do not need to declare them.
[Please be extra careful if you send direct low-level ros joint_trajectory message to a real robot. This can be very dangerous.]
I need some more investigation for your other question about moveit groups.