Basicly it's all abot how different the two sides (L/R) get compressed.
When linked 100 % both sides get compressed evenly when a signal in one side, either left or right, exeeds the threshold. In IND mode it's the opposite. So if you have loud sound in the left side and a quiet in the right, only the left gets compressed.
The filters are just like a normal side chain and filters out for example the low end in the sidechain, making the compressor react less to low end.
Soundwise I find that a link of about 70% can material a bit wider while still having the center locked. A link of 100 % keeps the center dead tight.
Each setting has it's own uses. But the good thing with the API2500 is that everything sounds amazing