Remember the Boy Scout motto "Be Prepared"? I believe in diversification. Yes, It is good to have some cash ready. But what about a run on banks? If you come walking out of the bank with your cash, there could be robbers or cops (civil forfeiture) following you home and ready to take your cash.
Well maybe you could put the money inside your wallet before walking out of the bank so the robbers won't see how much money you had 
And im pretty sure that nobody is this insane to following you all day
I could be wrong though
