Some exercises have a definite start and ending position ( Classic example is the Squat ) but others have such a small range of motion they feel more like you are just pulsing away at them. When I do shrugs for instance I feel that I can still pulse the weight a few short inches for many many reps.
Would I be better in these type of exercises just calling the set finished if my form deteriorates so that the fullest possible range of motion is impossible or should I instead just keep doing burn out reps?