Resurfacing flywheel on clutch replacement

I'm going to get a new clutch installed on my 89 RT4WD wagon. First time for it, with 128K on the odo. What's the story on flywheel resurfacing? Should it always be done, or can you tell by the condition whether it is actually required? What should it cost?
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I have done a clutch job before though (a long time ago when I did not know better and/or have the extra $50) without a resurfacing and it seemed to work OK. I'm sure that if you're into performance driving you'll find problems like slippage (which leads to heat damage to the flywheel and the clutch disc), vibration, etc. as the two dissimilar surfaces wear into each other.
Preety much the same issues with the clutch apply to the braking system.