Engine symptoms might be running rough or not at all. If a piston approaches an open valve then they can collide and break something.
The linked article describes different sensor types. A sensor can lose sensitivity, and you can test its operation using instruments, but you don't really know unless you test it in a running engine. And the engine won't run without a good sensor.
You need to drill into the specific make, model, motor, year to know the engine management scheme.
In the cases I know, cam sensor was used only for misfire detect and crude index while crank was for all timing. But who's to say what an Asian or European make might do?
In case the signals are hard to keep track of... The camshaft rotates once for every 2 turns of the crank. When assembling it may be necessary to rotate the crank one turn in order to sync it to the camshaft.
In past times those gears were marked Top Dead Center by means of notches, or circular indentations, etc.