It depends on how much slack. If its just a little bit loose then I would probably not worry about it. The transition to the slack cable happens instantaneously( I would say to the average human) and you never feel it go taught because the pushback on the rudder takes all the slack out in a millisecond. If its a lot of slack or if you are not sure, then I might consider an offset cable if for no other reason to keep from having the the cable spring taunt and jar the connections as it transitions back and forth from left to right. If there is enough slack that the cables are banging tight every time they transition back and forth its more tham likely shorten the life of something. Either the cable, the end connector or even the wood to control horn connection at the rudder depending on what sort of rudder horn you are using.