The bitcoin-mixer is a service, where your transactions are mixed with others’ ones, make the tracking difficult. The recipient gets the correct amount of crypto but from different addresses. This way you could protect your privacy, but may also be used for illicit operations.
Now a days tracking, monitoring tools are far advanced. The mixers can’t hide the path of the money. An expert talked about this recently, in the case of the stolen cryptocurrencies from Dooga exchange. Due to the blockchain, they could track the funds, and get them back.