Custom lightmaps question

I have a very basic question about creating custom lightmaps.

When I have an object that is for example very long in the y axis, and very short in the x and z axis, when I unwrapp them in 3dsmax, I get a lot of space “wasted” like you can see in the image.

My question is, when UE is creating the lightmass atlas, will be this “wasted” space really wasted? or UE will assemble them with other lightmaps so that space is not empty?

I ask this because it will take me a lot of time to cut the geometry in order to get a lightmap in a ratio 1:1…also I will be creating a lot of seams in an object where the light should be semaless…