When selecting steel channel sizes, there are several considerations that need to be taken into account. These include the load-bearing capacity required for the intended application, the span or distance between supports, the material and weight of the items being supported, and the structural stability needed. Additionally, factors like cost, availability, and compatibility with other building materials may also influence the selection process. Ultimately, the goal is to choose a steel channel size that can effectively support the intended load while ensuring structural integrity and meeting the project's requirements.