I am far from the expert, but for a given mass on a specific spring rate, there is a perfect amount of damping in each direction for managing high speed "bumps". These only really need to be adjustable for spring/damper configurations that are not optimized for the specific vehicle. (sort of)
Low speed compression damping, or the other hand is more about feel and handing in the corners.
If you do not have separate control for each of these, you really need to know what the adjusters you do have actually control on the shock.
Many single adjustables just increase or decrease everything and were originally designed to compensate for wearing internal seals over time. As the seals leak more, you close the bypass valve that was acting as a tuned leak when they were new. It also allows for a very small range of spring configurations to be optimized (somewhat) for the damper. Many people just crank these up which often makes things feel good and "tight", but actually increases lap times because the tire cannot follow the contours of the road properly.
2 way may be low speed bump and rebound (kWv3s definitely), combined high/low bump and rebound (DMS 50), or combined high speed bump/rebound and low speed bump (???).
3 and 4 can be whatever...
A good shock should tell you what each adjuster does, and ideally, provide a graph for each adjuster with speed vs. damping force.
