Do you know why IT folks hate personal devices? It is because it isn't IT's. We cannot make rules over what you can or cannot do with your equipment. We can't tell you not to download spyware. We can't tell you not to let your teenage daughter install cute cursor packs. We can't make you buy decent (or any!) anti-virus or security software or force you to stay up-to-date with patches.
And what plusses are brought by personal equipment? Well, we are now on the hook to support your own weird applications, like some graphics package that was downloaded off a Russian server and is entirely in Korean(*). We are now on the hook for keeping your eight-year old second hand clone (built by your son's super intelligent friend) running(*). We have to get the company VPN solution working with your weird combination of hardware and software(*). We are now encouraged to install "field evaluation copies" of corporate software(*) so you can do your job when your not-entirely-compatible open source package(*) causes hilarity.
And, when you ignore all this and corporate security is compromised and thousands of pieces of private data are "accidentally circulated more widely than initially intended", it is OUR ass on the line.(**) Frankly, if I'm the one getting canned when it doesn't work, it's MY F***ING network.
You bringing your equipment in may save you time, but it doesn't save the company any money.
(*) = actually happened to me.
(**) == happened to someone I know.