In a normal heart, they are usually not of concern. They usually happen because we expect them and because we are nervous during exercise, fear of having heart failure, overloading the heart, dropping dead, getting a heart attack, you name it.
However, in the absence of anxiety symptoms, they (especially if they are PVCs) can be worth taking seriously. From your previous posts, I understand that you are having some cardiac problems (high blood pressure, did you also have LVH on echo?).