Actually, I can’t, because I don’t really understand it;)
There are three modes as you can see, Subdivide edges, which subdivides long edges to make new geometry.
Collapse edges which collapses short edges if they get shorter than the resolution you have set in Dyntopo.
And Subdivide Collapse, which does both.
I usually leave it at Subdivide Collapse, unless with creasing…
Kent explains this better than I can, if you continue watching;)
