You mean putting all the eggs in the same basket? Of course it's not safe. Bitcoin is a great asset, but it is still in its early stage, which brings a high risk level. Besides that, eventually you will need money to cover the costs of your daily expenses, and if you have to do this when Bitcoin falls in price, you may regret not having saved some fiat.
Indeed! It's really a high risk. Bitcoin is so volatile and it is very possible that it's price will drop very low and that will let you lose all your money if you turn all your money into bitcoin. Aside from that, we need fiat for our daily necessities, there are only few stores who accepts bitcoin as mode of payment. And as far as I know, there are none malls who accepts bitcoin.