Well, the RG6 coax which is what most composite & component video cables are - they are measured with 100 feet and the results published. Many high-end projector systems (very sensitive) have 30-60 ft of good coax between the ceiling and the equipment with few problems.
SVideo cables are really 2 thin wires in 1 case and these dont do as well over 100 ft. Most installations limit these cables to .. 30 ft??
The shorter the better is the rule. But if you have a choice of something like 40 ft of speaker wire to a sub or 40 ft of interconnect, the audiophile view is that it's better to have a long interconnect, short speaker wires. (power signals have some extra issues over long runs).