Demo account is free to trade on. So you can easily practice on a demo account without the fear of losing.
Its advantage is that we can get the practice on demo account and can do real trading efficiently, demo account gives the confidence and awareness to do working.
Very good if newbie willingly spent time practice in demo account, at least six month, and look their performance during practice, don't jump to real account if still not sure in demo account they can manage money in uncertainty market conditionYes practice is very important in forex market. And demo accounts are just for that purpose. You can trade on demo accounts and can improve your trading.
from my experience would be:
advantage: learn and practice of course
disadvantage: (other than the feeling that its still not your money if you lose it) its still not your if you win it! I don't know if that makes sense... but.
Advantage of demo account is that you can learn and practice Forex trading on it, Also not only it helps beginners in learning but it help experts to make new strategies, and test those strategies in demo without fear of loss.
I think there is no such disadvantage of demo accounts but for those who show non serious attitude, They sure wast their time in it.