When should you use a Django signal instead of an explicit function call?

Uses Django signals selectively and makes transaction timing and side effects explicit.

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I prefer an explicit function call when the sender and receiver are part of the same application workflow. It makes ordering, inputs, failures, and tests visible. A signal is more appropriate when the sender should expose an event to optional or separately owned receivers without knowing them directly. Django's own guidance warns that signals can make code harder to understand and debug.

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Judgment about coupling, discoverability, post-commit work, idempotency, and extension points.

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Core answer
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Overview
Signals are useful extension hooks, but they are a poor default for an in-project workflow.
I prefer an explicit function call when the sender and receiver are part of the same application workflow. It makes ordering, inputs, failures, and tests visible. A signal is more appropriate when the sender should expose an event to optional or separately owned receivers without knowing them directly. Django's own guidance warns that signals can make code harder to understand and debug.
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A model signal runs around persistence, not necessarily after the surrounding transaction commits. If a receiver sends email, publishes a message, or starts later work immediately, that effect may escape even when the transaction rolls back. I use transaction.on_commit() when the effect should begin only after a successful commit, and I make the receiver idempotent because registration or delivery assumptions can still produce duplicates.

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Using post_save as the application's workflow engine.
Assuming a signal means the database transaction has committed.
Hiding required side effects in receivers that callers cannot discover.

When should you use a Django signal instead of an explicit function call?

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