The output margin is set to 16 pixels because sometimes when you apply textures to objects in Roblox, the texture fades a bit as you get further away, and sometimes you can see some color on the edges of the UV islands. This will just bake the light shining on the object directly onto the texture, so it will have a clear bright spot on it. Now, go to the render tab, find the bake drop down, chose what contributors you want to affect the baked texture (usually just diffuse) but decide what influencers you want, eg, a light source.