In relation to the needs of the organisation
You want to solve an in-house process or similar task.
The most suitable applications for Power Apps seem to be: filling leave request forms, booking company events, expense logging, requisitions, solving onboarding, IT requests, helpdesk, tracking the status of tasks, providing information, tracking the workflow of company processes, attendance, approving expenses, reviews, tracking the workflow of a product, forwarding to the next stages of production, inspection records, notifications of individual steps, access to information for employees going “into the field”, support at the customer (sees orders, can negotiate them), support inspection activities on site (e.g. developer on site – creating an inspection report, adding video, photos, … )
You already own sufficient licenses (for example for office 365).
Purchasing licenses (they are needed for both developers and users) and paying for them regularly will probably be the biggest cost of creating the app. But if you are already paying for licenses, this is a strong argument for deciding to take this route.
You are flexible enough and able to pay the cost of the app on a monthly basis.
The cost of a Power Apps app is pretty much based on a fairly complex licensing model, where it depends on the specific app and its purpose. The customer must be prepared to pay for those users when the number of users increases. When new functionality is needed that is not covered by existing licenses, those licenses need to be added.
The application is not critical to you for speed and availability
I.e. uptime/high availability is not important to you. – You do not have full control over the environment where the application is deployed. The environment is constrained by a lot of limits, number of actions, requests, speed limits, … resulting for example from licenses. The environment is updated from time to time. New or changed platform functionalities are deployed on it. Therefore, it is necessary to take into account that some functionalities will not run very fast and will not always be available (even if only minimally). Applications where you would be bothered by a response time of even a few seconds are not a good candidate for Power Apps.