A practical view
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.
The useful question
Shopify decisions become easier when the team names the actual constraint: customer experience, operations, data, permissions, or maintenance. The right implementation follows from that situation.
Keep the boundary clear
A theme change, an existing app, a Shopify Function, and a custom app solve different kinds of problems. Choose the smallest tool that can carry the requirement without hiding important edge cases.
Make room for the next decision
Good technical work is clear about what it solves, what it leaves alone, and what the team should watch as the store changes.