When attacked, it will give chase with the same speed as the player, making it hard to get away from. It has 1500 life and does 70 damage. It is a bad idea to attack it, as it doesn't drop lava hearts, and it will waste your time and hp doing so. The only reason that you would attack it is if you want to tame it. The only specific case for killing it is when you run out of food in lava biome and for some reason. Then the only chance to stay alive will be to find and trap some of these dragons in walls and then kill them.
Please note, that even being neutral this mob can break your buildings.
Baby lava dragon is the fastest vehicle in the game.