User blog comment:RandomGuy96/So how do planetary defense cannons work?/@comment-4950455-20130127221231/@comment-3217145-20130204105531

But you'd be splitting your attention between twice as many targets - a fleet's worth of ships and a bunch of planet-based cannons. You have to assume that you wouldn't just fire one shot at one cannon and be done, they're PLANETARY Defense Cannons, so there would be a lot of them. While you're dividing your attention between two groups of targets, the enemy fleet is devoting 100% of its attention toward you. Unless you have a vastly overwhelming force, you wouldn't come out of that encounter looking too good. And if you have a vastly overwhelming force, the PDC's wouldn't matter anyway, since they're not supposed to hold off entire fleets.

Think of it this way. There's a Banshee shuffling around way off in the distance, and three Brutes right up in your face. Are you going to try shooting the Banshee as a precaution for later, or do everything you freaking can do survive against the Brutes?

And as stated by others, if there were no Brutes (i.e. defending fleet), the Banshee (PDC) is irrelevant. Of course you'll have no problem taking it out with a full squad (invading fleet). But say you don't have a full squad; say it's just you against the Banshee (i.e. not an invading fleet, just some pirates). Say you don't have any guns or powers (heavy artillery from cruisers and such), you only have melee (frigates and fighters). Do you charge the Banshee and start punching her in the face? No you do not. This is what the PDC's are meant for, flyswatters for relatively small forces threatening a planet's surface. They lose to an entire invading fleet, but that's what defending fleets are for.