I took my car into my auto mechanic, and they told me that my serpentine/drive belt needed immediate replacement due to dry rot. I let them replace it for me, but afterwards I looked more closely at their vehicle report, which had photos for each of the service items. The drive belt in the image does not appear to have cracks. Was I just cheated by my mechanic? Or can dry rot of a belt be an issue, even if the belt is not visibly cracked?
In a word,
Cracking does not indicate a worn or "needs replacement now" condition.
Most serpentine belts will have cracks on the ribs going across (perpendicular) to the ribs seen by bending the belt with the ribs outward. This is perfectly normal and NOT the way you check the belt for soundness. The real way to check it is with the use of a Belt Wear Gauge. The belt will be worn through wear, not if the ribbed side is cracking. A worn serpentine belt will most often start slipping before it will break or come off of their tracks. You'll usually start hearing the power steering or alternator squealing first. Some belts may get worn out through stretch and exhibit the same symptoms. Some vehicles have a stretch gauge built into the tensioner pulley, where there will be a notch on one side and a pointer on the other. When good, the pointer will be within the area covered by the notch.
As an anecdote, I had a Jiffy Lube guy yell at me that my serpentine belt was done because it had cracks on it. (NOTE: I was in an HOA which wouldn't let me change my own oil ... argh.) I politely told him it was fine and he tried to lay all of his worldly knowledge on me. I drove that belt for a good while after that (read: years) before it was changed. There wasn't an issue with it ... it just had cracks in it.
If the belt has rubber chunks missing, then it'd be time. If the belt is stretched beyond service limits, it's time. If there are threads showing, it's time. If there's cracks? Not necessarily time. IMHO, if cracks were all that was wrong with it, they took you for a ride. PS: I don't see any cracks in the photo, either. I also don't see what I'd consider excess wear.