Given a flow on a 3-dimensional closed manifold and a link of periodic orbits, we may consider all periodic orbits of the flow that are unique in their homotopy class in the link complement. In my talk, I will explain a result that says that for a $C^{1+\epsilon}$ flow, a sequence of such links can be found for which the exponential growth rates of the orbits with the above uniqueness property approximate the topological entropy of the flow. This result has applications in the symplectic dynamics context. It is an important ingredient in the proof of a result (jointly obtained with M. Alves, L. Dahinden, and A. Pirnapasov) that generically the topological entropy of 3D Reeb flows is lower semi-continuous with respect to the $C^0$ distance on contact forms. Another application deals with certain lower estimates on barcode entropy, a notion recently introduced by Cineli-Ginzburg-Gurel.