Intuitively, running a non-exit Tor node should bring the benefit of plausible deniability that a packet originated from your device.
Unlike exit nodes however, you would not have to worry about illegal content requested in the clear by your computer.
So it seems that running a non-exit node would have only benefits (not considering the increased traffic caused by this; assuming Tor does not have any exploitable security vulnerabilities in the relay code to compromise the relaying computer).
Does operating a non-exit relay node have any security-wise or legal issues I am not aware of?