Strategy games have kept replay systems long after video capture became trivial. The reason is that a replay file is not a recording of a match but a script for recreating it.
Deterministic simulation makes replays cheap
Most strategy games advance their simulation in fixed steps, and given the same starting conditions and the same commands, the outcome is identical every time.
A replay therefore only needs the starting state and the timed list of player commands, which is a very small file compared with any video of the same match.
That property is a byproduct of how multiplayer works in the genre, since clients that simulate identically only need to exchange commands rather than full world states.
Replays enable analysis video cannot
Because the match is re-simulated rather than played back, a viewer can move the camera anywhere, follow any player and inspect information the original participants never saw.
Coaches and competitive players use this to examine decisions from the opponent's perspective, which is the only way to understand what information a choice was made with.
Fog of war can usually be lifted in review, turning a match into a study of what each side knew rather than only what each side did.
Patches break stored replays
The same fragility that makes replays small makes them version-locked. Change a unit's speed or an ability's cost and the recorded commands produce a different match.
Games therefore stamp replays with a version and refuse to load them under a different build, which is why a library of old replays becomes unplayable after a balance patch.
Some titles maintain the ability to run older versions specifically so archives remain accessible, but that carries a real maintenance cost.
Replay data feeds anti-cheat and balance work
Because command streams are compact, developers can retain them at scale and examine aggregate behavior across many matches.
Patterns that look ordinary in a single game, such as inhuman timing consistency, become visible when the same player's commands are examined across a season.
The same archive supports balance analysis, since designers can ask how often a strategy appears and how it fares without instrumenting the live client further.
The system shapes the community around it
Accessible replays let players share matches, produce analysis and build tools that parse command streams into statistics without any special access.
Games that expose the format openly tend to grow an analytical community, which sustains competitive interest between official events.
Where the format is closed or the files are unstable across versions, that layer of activity does not form, and match analysis stays limited to whatever video anyone happened to capture.