If the helmet fits well on the head (for example, when you feel a slight pressure on the cheekbones), it is not necessary to fasten the straps .
It does not matter to wear it without fastening, because it is very difficult to get it out of your head in case of an accident .
If you do not fasten the helmet, it is very likely that during an accident it will be thrown from the head and will not fulfill its protective function .