Since Im still a complete noob all I can go on is what Im told. I have a friend who switches strings every 2 years or so NO MATTER WHAT THE CONDITION. He says (as well as what Ive read) is that strings will stretch over time. One guy even suggested keeping aside a special arrow that has a mark on it from when you put a fresh string on. every now and then he will check the arrow and once there is something like a 1/2" difference is when he changes it.
Cables, as Im led to believe, NEVER need changing (unless of course they break
.)
But again, this is not my experience, just what Ive read and been told.
Brian M.