Excerpts from GoldMoney's Ultimate Gold Buying Guide:
Gold bars can vary in size from tiny 1-gram ingots (sometimes called “wafers”) all the way up to the “London Good Delivery” 400oz bricks held in central bank vaults around the world. Though Good Delivery bars are described as weighing 400oz, they are permitted to vary in gold content weight between 350 oz and 430 oz —but they must have a purity of at least 99.5%. Perhaps the biggest drawback of owning gold in the form of coins and bars is the lack of liquidity when compared with third-party storage on an internet platform. If you ever need to sell your gold in order to raise cash for whatever reason, it’s more time consuming to do this by selling to an actual high street dealer than it is if you have a web-based ownership platform.
In addition, there may come a time when online gold payments for goods and services become common place, in which case choosing to buy gold online could be the wiser choice.