It means that a PAYE taxpayer who has <€3174 of self employed income can return this income without having to register as self employed. It means they can still just get a P21 balancing statement every year, rather than having the hassle of preparing accounts, filing a form 11 etc...
So, there's no free lunch, don't panic! However, whether or not the majority of people giving grinds etc.. are actually declaring this income, that's a different kettle of fish entirely...