When comparing the proper position for spotting different exercises, you can conclude that, in spotting any exercise, it is important to

Have proper posture which will minimize your chance of being hurt if the need arises for your to help the one for whom you're spotting the exercise.

Moreover, it's also important that you pay close attention to the person you're spotting to see and check if he or she will need help anytime soon to be spotted or not. This is something many spotters can miss and is at the same time a crucial aspect of spotting.

Well if you pick a machine to work on and that's gonna be your exercise if you don't stick to that machine your muscle strength your muscle mass rather will change because you haven't been doing it you change something in your exercise routine which changes your body's form of dealing with things for example you might become weaker or stronger depending on what kind of exercises you do in whether or not the machine you picked actually your muscles grow.

Olfactory epithelium i believe