User blog comment:RandomGuy96/So how do planetary defense cannons work?/@comment-5436239-20130127223836/@comment-5436239-20130127234149

You are still misinterpreting what I am saying. These weapons, like I said, are only considered fail safes in the instance of total warfare or a large fleet.

If a ship is focusing on a fleet, most personal are worried about what the other ships are firing. Every now and then, a projectile will get through and mess them up. Most of the time they will dodge these shots, then get pulverized by the other fleet. They can't focus on two things at once.

Now, when do PDCs become ultra effective? Slavers, raiders, and the threats Horizion was worrying about. These guys are coming in for resources, slaves, and maybe even a new base of operations. They don't want to destroy it, and they are most likely incapable of doing so. They come in, and surprise! They get shot down.

In large battles these weapons are mostly ineffective, but still valuable because enemy ships, IF they want the base, prisoners, Intel, etc and will be shot down. However, now that they are in orbit, they can take out the cannons with smaller weaponry without fear of massive damage.

There are many more uses than disadvantages for the cannons, especially in the Mass Effect universe. Yes, the cannons are stationary and in Total Warfare or in the takeover of a planet, very vulnerable. But if it is a more likely case of raiders, a cheap slaving fleet, or an Intel/Personnel/Tech. grab, these weapons will tear apart the ship that is either incapable of destroying the cannons, or can't risk destroying them.

They are invaluable assets, that is undeniable and I hope that is clear now.