A custom plugin is not automatically better than an existing product.
If a mature plugin already solves the requirement reliably, has a reasonable license and integrates cleanly with the website, using it can save time and reduce maintenance.
Custom development becomes useful when the workflow is specific, multiple plugins are being forced together, the admin process is inefficient or the business needs a feature that does not fit existing products.
Examples include custom client portals, approval workflows, structured imports, internal dashboards, specialized pricing logic, unique directory systems and API-driven operations.
The architecture matters. Business logic should not be placed randomly in theme files or code-snippet tools when it needs to survive theme changes. A dedicated plugin can provide clearer permissions, structured data, settings, validation and upgrade paths.
The decision should be based on long-term ownership and complexity, not on a preference for custom code.