Permissions are the boundary between an app and the rest of your device. Nothing reaches your camera, microphone, photos, location or contacts until you say yes, and that decision is remembered.
The trouble is that a refusal is remembered silently. Months later a feature fails with a vague error, and nobody links it to a prompt dismissed while distracted.
Modern systems add granularity: location can be while-in-use only, photos can be limited to selected items, and notifications can be allowed per category. Apps written for older rules sometimes behave oddly under the tighter options.
Reviewing permissions per app, rather than per feature, is the fastest way to find the missing yes.