double differentiation is used to find out if a curve has a maximum, inflection point or minimum. It is also used to determine acceleration if you have a relationship between distance x travelled versus time t, e. g., x= f(t) = -2t^2 +4t +24. f '(t) or the 1st derivative would provide the velocity dx/dt at time t, while the 2nd derivative f ''(t) would provide the acceleration at time t.
dx/dt = -4t +4
d'x/dt = -4
hope this helps.