Why so much seam sealer?

In my 72 Swinger there is a absurd amount of seam sealer everywhere in the trunk. My rear window leaked at some point and rusted some areas in the trunk. I am now removing the seam sealer to insure all the rust is gone. My question is do i need to put all of this back on. The had seam sealer smeared where seams were not even near. Also how do you dress up your trunk? Is it painted like the car or some trunk splatter paint?
Thanks,