yes its safe to turn on. but make sure you know what changes you do in developer options. developer options are for developers to make app or tweaks for the smartphone. there is no useful option available for us, the usual users. there are few options which will lead to weird stuff!!!
Turning on Developer Option is totally safe until you don't mess up with the software and features inbuilt in it.
Its mainly for the features that can be used only if you enable them on your own. Like changing the animation scale, Turning the mobile data always on, making separate volume controls for Bluetooth devices and mobile device, usb debugging, etc,.
Its turned off by default because as the name suggests Developer, so it is mainly useful for the people active in that area. Normal person need nothing in that option, that's why it is kept hidden.
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