It decreases the frame rate? It shouldn't... I dunno. Thats the best method for scrolling in TGF. Maybe it has to do with your computer - what are your specs?
Have you monitored this with a framerate program while playing?
It really shouldn't: my PC is: 2.5 GHz, ATI Radeon 9600, Windows XP.
I haven't been monitoring it, but I can see it on other active objects that stick to their places - their animation speed also decreases, scrolling is slow, but when it is not scrolling the other objects 'Come to life'