They make the server a pain: a portion of the server is constantly afk in the skybox, caber demos abuse it with a shield to get air by grappling on the skybox (meaning they can forgo the sticky jumper for a shield), snipers have easy access to the train and ramp (obviously not so much the ramp but you get the idea), frequent spawncamping since it has facilitated travel to the skybox, and most importantly, your side of the battlements (where the small health packs are) is not safe anymore as people can instantly access it using the grapple hook. I'm sure 90% of the idle regs will agree with me here.