Tailoring the rheological properties of soft composites at molecular level is critically important for optimizing their performance and enhancing the range of their applications. In this context, a formidable challenge is understanding the role of macromolecular architecture on topological constraints and the resulting network dynamics. Ring polymers represent a unique case because of the absence of free ends that mediate conformational arrangements in a topological entanglement network. Here, we briefly summarize the current state-of-the-art regarding the rheology of these loopy structures. We show that they exhibit unusual nonlinear response in shear and, especially, in extension because of loop interlocking. Then, we focus on the role of small amounts of ring polymers or other loopy macromolecules (such as self-associating chains) as effective reinforcing agents when added to entangled linear matrices. These purely entropic phenomena can be understood by invoking the (coherent) constraint release process on the rings due to the escape (unthreading) of linear chains, while some consequences on the nonlinear rheological response are also presented. The punchline is the emerging ability to selectively tailor the rheological properties of a wide range of polymeric networks with loops and, at the same time, provide insights on the physics of the constraint release process.