I chain vape whenever I can - not just for the nic, but because it quells my crazy sweet tooth (lost about 40 pounds since I started a year ago) and it's fun! But I've also gone for long periods (4+ hours) without vaping at all, and surprisingly without going through the withdrawal symptoms that I got when I used to smoke - like getting mean, grouchy, cranky, irritable, fidgety, losing focus/concentration, etc.
I don't think there's any harm in it (my health is better than ever), but you do have to pay attention to any symptoms of getting too much nic (pounding headaches, palpitations, etc.), which can be harmful. This new delivery system is quite a bit slower than smoking, and sometimes you have to slow down a bit to give it a chance to catch up. Also, drink plenty of water, cuz headaches could be due to dehydration as well (the liquid is known to cause dehydration)...plus it flushes down any sediments from the liquid that can cause sore throats, leather tongue, bad breath, etc.