Yes! heed this man's words. I used to do this all time, but after being killed one too many times when the ai manages to get past my border worlds, I tend to leave turret defences in place and just unlock new ones if I run out. Nothing wrong with deleting old turrets of course, but just be aware it can be a little risky - at the very least i'd always leave the turrets on the wormholes and command centre on your home-world.