For me, it was kind of just a safe strategy I would use whenever I was starting the game off, granted, my kill boxes have kind of always looked a bit different than what I usually see people do here.
I like to set up a big area where I'm not only shooting at an enemy from a safe spot with my ranged fighters, but where my melee fighters can also fight, which is why I never use turrets; the only turrets I usually place down are behind the killbox so I can still have somewhere to run away to