A striking number of released independent games started as entries in a weekend competition. The format happens to answer the hardest question in early development.
The hardest question is whether the idea is fun
Design documents cannot answer that. An idea reads well or badly on paper for reasons that have very little to do with how it plays.
The only reliable test is a playable version, and the value of that version comes from existing quickly rather than from being well built.
A jam forces exactly that, since a deadline measured in days makes anything other than the core interaction impossible to include.
Constraints remove the expensive decisions
Jams usually impose a theme and a duration, which eliminates the open-ended planning that consumes so much time at the start of a project.
With scope fixed externally, the developer spends the available hours building rather than deciding what to build, and the result is a finished small thing.
Finishing is itself the skill being practised, and a developer who has finished twenty small games has a very different sense of scope from one who has finished none.
Feedback arrives immediately and at volume
Jam entries are played by other participants and by people browsing the event, which produces reactions within days rather than at the end of a long production.
That feedback is unusually honest, because nobody has paid anything and expectations are calibrated to a weekend project.
A prototype that people keep playing after the novelty has passed is a genuine signal, and it is the signal studios use to decide what to expand.
Expansion is a different project entirely
A jam game proves a mechanic works for ten minutes, which says nothing about whether it sustains ten hours, and that gap is where most expansions fail.
The prototype code is usually discarded, since it was written for speed and carries assumptions that break the moment the scope grows.
What carries forward is the knowledge of what was fun and why, which is the expensive part to acquire and the cheap part to rebuild around.
The format also builds the things around the game
Repeated participation produces a network of other developers, an audience that has followed several projects, and a portfolio that funding bodies can actually look at.
Those assets are difficult to assemble deliberately and accumulate naturally through showing up, which is why the route appears so often in studio histories.
The jam is therefore less a shortcut to a game than a low-cost way of running many experiments until one of them is worth committing years to.