the effect it could have is that genuinely poor people, who dont have access to a bank account could be hit. i know a few like that, salt of the earth types, everything done in cash. but i think overall its a good idea. lots of people use cash/chequeing shops for genuine reasons, i have done myself a few years back.
it wont prevent 'professional' criminals however, who will just use some scrote to weigh it in for them. that or melt it down and sell on the blackmarket.