Not just for BVR, AEW (or ground based radar) can guide fighter to their target, because fighter radar coverage is facing forward (a little bit to the sides, up and down) so there is a lot of blind spot, AEW can guide fighter to intended target via dodgy flight path so it won't be easily detected by the enemy and surprise them from the sides or from behind).The lesson in pitch black practice a few years ago taught us that without the support of AEW&C we always lose in BVR games with several other participating countries even though we use SU30/27&F 16, maybe that's our consideration for the acquisition of AEW&C to increase BVR capabilities in our air fleet
Useful for close - medium range engagement and giving more situational awareness.
You know just like those giant humanoid mecha anime, the crews on the mothership that is monitoring the radar screen can warn the mecha pilot that there is enemy approaching from behind to sneak attack.
So if our sukhoi that is only relying with onboard radar vs enemy team that have more advanced sensors / supported with AEW etc, it will be challenging for air combat scenario.