Well, according to some researchers, Keeping AirDrop on Mac unnecessary can have some security issues as AirDrop lets you share any document, file, video, photos with another person against their mobile number and email address. Keeping it on every time can lead hackers to do some scam if they are nearby your device. It is also true that MAC ensures safety with cryptography, but for some, it can be easy to crack that cryptography, so one should disable it when they are not using AirDrop. But there is nothing to worry about too much, but for some reason, you should always maintain your privacy.