It depends on what type of wallet are you storing up your bitcoins, If its on an online wallet then sure it has big risk on lossing it because you dont have its private keys unlike on pc wallets and cold storages. Web wallets are only good for faster online transactions.
Agree, web or online wallet are good only for fast exchange or payments onto services online or buying up something but its not really safe to put up your bitcoin on their but there are still good web wallets like blockchain which do have a good security on their wallets and i didnt even heared about any complain of being hacked or lost bitcoins into someone.