yes it is the best strategy to save you money and savings. My favorite sentence "Do not put all egs in one busket". in another word it is diversification. Exchanges can be hucked by huckers, money from wallet can be stolen. So hold coins in multiple wallets it is smart solution
Yes that is too much important, i think we should distribute our money in different wallets, specially if we are using online wallet then we need to be too much careful, because hackers are always there who always trying to hack your account.