I write these guides from the situations that come up in real Shopify work. The answer is usually less about a fashionable tool and more about choosing a boundary the team can live with.
Start with the job, not the label
A custom theme is useful when the storefront needs a structure, interaction, or editorial system that a strong premium theme cannot support cleanly. A premium theme is often the better choice when the store needs a reliable foundation, sensible merchandising tools, and room for measured refinement.
Ask what must be different
List the customer journeys and the store-team tasks that matter most. If the difference is mostly visual, a premium theme may give you more speed and less maintenance. If the difference is how the store explains, groups, or sells the products, custom theme development may earn its place.
Choose the smallest sound foundation
The right answer is not the most bespoke answer. It is the foundation that leaves the team with a store they can understand, extend, and operate after launch.