The Frog ascending system was developed in France and is the standard in most of the world. It is light, fast at mid-rope maneuvers, and easy to wear while caving. It is not as efficient as ropewalking systems.
The Mitchell system is a ropewalker system that is quicker to get on or off the rope, and faster at mid-rope maneuvers than a traditional Ropewalker system. It is also very fast and efficient at down-climbing.
If a changeover from ascending to descending, or rappel to climb is needed, then something has probably gone wrong, but having the skills to change direction is critical when a rope is rigged too short or a hazard is encountered.
Deviations are used in alpine rigging to direct the rope away from hazards such as edges, loose rock, and running water. Crossing them is usually straightforward, but there are a few tricks and techniques that will help.
Knots should be avoided when rigging caves, but occasionally a worn spot must be isolated or a rope is too short and the rope and rigging on-hand may require a knot be used temporarily. The skills to cross mid-rope knots is something that should be in every cavers repertoire.