Spamming c-sites is not allowed. I've seen somebody [I think it was hobo], who built a weapon rack right at the flag, and used to to throw and endless supply of throwing lances...
I could see forward bases being useful in maps where you pretty much locked down an area and it's a pain in the ass to get to the flag [I could think of a couple of maps that fit that description], or for defense in spawning closer to the flag.
Frank, what I meant was that you build the thing once, and it stays there until somebody destroys it, which is the part that seems like an exploit/bug. One map, I set my point to an attackers forward base, and the next round, I was on defense, and it sucks to res surrounded by a swarm of enemies -_-, that and depending on its location, could royally fuck defense over [I could see a guild build a forward base at the flag and delay capping it just so they instantly spawn there].