An internal leave-request app is a classic Canvas App reflex: someone needs a simple form and an approval step, so a Canvas App gets built, and a Power Apps license gets budgeted per user.
If your employees already carry Dynamics 365 Enterprise or Premium licenses (Sales, Customer Service, Field Service and similar, not the Professional or Team Members tiers), that budget line may not need to exist. Those licenses include unlimited internal Power Pages websites, as long as the site runs in the same environment as the licensed D365 app. The same leave request, the same approval step, built as an internal Power Pages site instead, costs nothing extra in licensing.
Power Pages isn't a downgrade for this kind of task. Forms, lists, role-based views, and approval workflows cover most internal self-service scenarios, and there's no app to deploy to every device, a browser is enough.
None of this is an argument against Canvas Apps everywhere, it's an argument against reaching for one by reflex when the license for something else is already sitting unused.
Where to go deeper: For the full Power Pages vs. Canvas App cost comparison and what else is included out-of-the-box, see Power Pages License Value: What's Included Out-of-the-Box?
I map exactly this kind of licensing fit in an Architecture Workshop, before a single internal tool gets built twice.
