Reusable elements are pivotal for cutting down on redundant UI (and workflows, as described above). If you find yourself needing similar or exactly the same UI in multiple places, a reusable is the way to go. You may need to use conditional statements to show/hide elements or on workflows if the same reusable needs to be used differently in different places. For example, if an Admin and a Standard user both need access to the same popup on their respective dashboards, you may need to hide some of the popup's fields for the Standard user. Ultimately, it's a judgment call as to when there are enough similarities to warrant using a reusable.