I've experienced what
tFUnK has as well. Sometimes, maximum small/small chain length will be too long for the specific derailer-and-cassette combination, especially if the large sprocket is at or even just near the derailer's largest allowable. This is not a problem on most of my bikes, but is a problem on a few.
As an extreme example, I'm using an old 105 RD-5600 on a '70 Peugeot, but the derailer's springs appear to be fairly loose and the B-spring won't keep it out of the 28-tooth large sprocket with the chain length that I prefer. I could have significantly shortened the chain to get more cage movement in the larger sprocket, but that brought other side effects. I ended up using a road link to lower the derailer down so that I can run a longer chain and still have the derailer clear the large sprocket.