Adding a second camera to a live broadcast introduces a problem recorded production does not have. The choice between them must be made in the moment and cannot be revisited.
The cut has to happen before transmission
In recorded work the decision is deferred. Both angles are kept and an editor chooses afterwards with full knowledge of how the scene developed.
A live broadcast has no afterwards. Only one image can be sent at a time, so the selection must be made while the event is still unfolding and its outcome is unknown.
That is what a switcher does, combining the sources into one output stream and giving an operator a single control surface for choosing between them instantly.
Anticipation replaces selection
An editor selects the best available shot in hindsight. A live operator must predict which shot will be best a second before it becomes so, and commit to it.
Cutting after something has happened means the audience sees the reaction rather than the event, which is why live direction depends heavily on knowing the format's rhythm.
Experienced operators watch the sources that are not on air more closely than the one that is, because the next decision depends entirely on what is developing elsewhere.
Preview solves the framing problem
Cutting to a camera that is repositioning produces a visibly unstable shot, so switchers separate the output into a programme feed and a preview of what is queued next.
The operator sets up the next source on preview, confirms it is framed and stable, and then transitions, which makes the change a two-stage action rather than a blind one.
This is also how camera operators are given time to move, since a shot that is not on preview or programme is free to be repositioned.
Synchronisation is a technical requirement
Sources arriving with different delays cannot be cut between cleanly, because switching would produce a jump forwards or backwards in time at each transition.
Switchers therefore align sources to a common timing reference, and mixing devices with very different processing delays is a recurring problem in improvised setups.
Audio is handled separately and continuously
Sound is generally not cut with the picture. A microphone stays open across camera changes, because switching audio at every cut would break the continuity a viewer relies on.
That separation is why live productions run an audio mix independently of the video switch, and why the two roles are usually held by different people even on small broadcasts.