A gy should have a rag in one hand and give those zerks a swipe so you don't pump gritty old grease setting on that little ball right into the joint. Enough dirt gets in as it is, I usually wipe off any excess if I can after I take the hose loose.
I have never tried them, but would think if they are tight enough to stay on I would have trouble getting them off. If they were easy to take off, I would be losing them all the time.