Reach is an important factor when it comes to taking out your opponent. The range of your weapon lets you hit a target from a certain distance. If this distance is greater than the range of your opponent’s weapon, then that puts you at a major advantage. Not only does this occur for melee weapons, but also other weapons such as firearms, rockets, and artillery.
Regardless, for melee weapons where one hit can easily do massive damage, reach presents a huge advantage. The person without the greater reach must come in close, but it’s game over if they get hit while coming in.