As the topic says, my '74 2.0L ECU adjustment knob has no "clicks". It just turns freely from one extreme to the other. It does produce a small effect on idle when turning from end to end. Is something broken inside and could this affect its optimum operation??

Sounds like something is broken. You should be able to easily feel a click when moving it to each position. The effects should be pretty noticeable in that when you turn it counter-clock wise it leans it out which at some point should cause the idle to hunt.

The detents or clicks are just for referencing. Before you start to adjust the know it's important that timing is correct, fuel pressure is correct, air intake adj screw on the TB is set to best idle speed and of course no other gremlins like vacuum leaks. You need to allow several seconds between movements of that ECU knob.