I did the annual pre-season tune and checkup on a customer's bike today. The bike is fifteen years old, with Shimano Ultegra road shifters, and the cables had never been changed.
So?
So in the past 2-3 years, I've worked on four or five bikes with Shimano road shifters (Ultegra and 105), where the shift cable has parted inside the shifter. In some cases, I was able to remove the short bit of cable and get the shifter working again; in others, I could not, and the shifter is gonna shift again, quoth the raven, nevermore.
I've resolved to tell folks with older bikes with Shimano road shifters that I recommend changing the cables, based on these experiences. My customer today agreed, so I changed 'em out (internally-routed shifting, so a PITA, but that's a rant for another post). The old cables are in the picture above. There's a terrible blow-up below:
The lower cable is for the rear shifter, and you can clearly see the frayed cable. It was a matter of time and use before this let go. The cable above is from the front shifter. It's used much less frequently, but the careful eye will note that the black Teflon covering is wearing away a short distance down the cable.
The older Shimano shifters have the cable take a hard turn inside, and I'm sure that's what's causing the wear. I haven't seen the same problem with SRAM stuff, and I doubt it will be a problem with Shimano GRX shifters, partly because they're newer (after all, this takes a decade or so to happen!), and partly because the don't make the same demand of such a hard turn on the cable.
(But it WAS gratifying to have my recommendation so clearly confirmed!)
So if someone tells you to change out your old cables, the like of this is why.
*All is not necessarily lost if the shifter dies. Even if the speed combination is discontinued by Shimano, I've had good success with two Chinese manufacturers, Sensah and L-Twoo. So your 3x9 drivetrain may still be able to be saved.