Of course a cable won't stop anyone who is out to steal your bike, it's mostly a way to keep the helmut there if you wanna go somewheres for a short time. When they are out to steal they will, in that case only theft insurance can help. Plus a cable log will deter the average joe from just picking it up and walking away, it does for 10 million bikes that use them, it won't stop the professional thief but it will deter the average joe, at least until your on your bike again and rolling
Never understood why people think their bike is "safe" with a U-Lock, cable lock or a disc lock. If the lock isn't secured to something immovable it's NOT safe. Even then it's not safe from an experienced thief.
There are plenty of security videos posted online of parked bikes being boosted into vans and trucks. Two guys could be gone with your ride in a matter of seconds unless you make things a little more difficult for them. The CBR is even lighter than the Ninja250 and even 2 scrawny guys could lift it into a vehicle in no time.
Bike security is all about making things look like it's not worth a thief's time so they will go looking for easier prey. A simple chain or cable lock SECURED TO A POST is usually enough to make thieves pass you by and hope for an unsecured disc-locked bike on the next street.