You can not carry coins for huge amount. Huge cash in coins form will be too heavy in weight. If all things available in coins, then coins will be in circulation. But we cannot get all things in a few coins so Currency notes are in circulation.
In some aspects the coins are better than the banknotes. Firstly coins are far more durable than the banknotes, coins survived for the thousands of years rather than banknotes which lasts a few years in circulation.
Coins are made from different metals, hence the value of coins are nearly equal to their face value and higher denomination coins are made from the metal of higher cost but the banknotes are just the pieces of papers.Counterfeiting of coins is not much easier than the banknotes, which can be easily counterfeited.