Should these be changed at the beginning of every season?
yes
.
I only change mine when they show signs of wear or damage. Sometime have replaced just one cable. Never thought about just replacing them as a preventative measure.
Huh?! Nope - never change them (or even tires) when they look worn, time to start shopping for a new bike 
If it’s STI shifters, you should change them, if it’s just bar ends, wear them out.
Great question.
Last night I watched three documentaries on The History Channel about air disasters. Metal fatigue, improper maintenance, pilot error… These factors cost thousands of lives due to preventable mistakes.
I look at bike maintenance exactly the same way.
Gtingley recently posted something about a rider having a *fatal *accident due to a fork steer tube failure ***after being notifyed of the problem during maintenance at a bike shop. ***
So, I look at cables and bolts on a bike like space shuttle “O” rings from Morton-Thyokol.
You should inspect these systems frequently. A slipped rear brake cable could put you in the middle of an intersection inadvertantly. Extremely dangerous. Inspection is key to the maintenance of your braking systems.
Look for dirt, frayed cable ends and compressed cable housings. When you see these symptoms, act. Replace or adjust as needed.
When dirt contaminates the cable/housing system try to clean it out. If it won’t come clean then replace it.
The key here is vigilance. Keep an eye on the stuff. If you consider replacing it, then replace it.
Play it safe. Your bike will run nicer and it will be safer.
Happy holidays.
I have never ever heard of a cable snapping on a bike during a ride - slipping? Sure, I have not once ever in all my years on a bike heard of anyone being in an intersection due to a bad cable - poor shifting, sure. Never anything worse. While agree with you on metal fatigue - and have had handlebars and stems crack under me, the cables are a strech (no pun intended).
SHIFT cables should be changed as regular care for a bike, the new 10 speed systems have less than a MM tolerance to shift well, and they like a cable to be smooth in function. Many times you dont feel your cables going bad…but you sure notice the new ones.
I change cables at the begining of each season. During the season, when washing the bike & cleaning the drive train I check the cables to make sure everything is cool.
At least once a year. I have seen the cables break, also bars, frames, etc. They do break down. Don’t buy a nice bike and then cheap out on the maintenance.
i change my ever season or 5000 miles witch ever come first…i always keep a few spare cable UNDER MY DOGS COOKIE BOXES…??? that dosnt make any sense???