  Quantum walks are widely and successfully used to model diverse physical
processes. This leads to computation of the models, to explore their
properties. Quantum walks have also been shown to be universal for quantum
computing. This is a more subtle result than is often appreciated, since it
applies to computations run on qubit-based quantum computers in the single
walker case, and physical quantum walks in the multi-walker case (quantum
cellular automata). Nonetheless, quantum walks are powerful tools for quantum
computing when correctly applied. In this paper, I explain the relationship
between quantum walks as models and quantum walks as computational tools, and
give some examples of their application in both contexts.
