Start with what the visitor needs to do
If visitors need to understand your offer, read resources and contact your team, a well-structured website may be sufficient. If they need to manage records, approvals, subscriptions or orders, you are describing an application.
Accounts change the scope
An account is more than a login screen. It introduces password recovery, authorization, session behavior, account deletion and support processes. Different user roles make the access rules more important, not just the navigation more complex.
Content and operational data have different needs
Marketing content often benefits from a CMS and a publishing workflow. Operational data needs validation, access controls and a clear source of truth. Keeping that distinction explicit avoids treating a page editor as a business database.
Many businesses need a deliberate combination
A SaaS business may need crawlable public service pages and an authenticated workspace. The public site helps people evaluate the offer; the application delivers the service. Each needs its own performance, security and accessibility checks.
Choose the smallest system that solves the job
Do not add a complex application solely to appear sophisticated. Equally, do not force a transactional workflow into a set of forms and email threads when users need reliable state. Document the task first and select the architecture second.