I'd guess you're talking about their PWL (Pre-emptive wear levelling) system? I believe (but I haven't seen much about it nor investigated too much myself) that all WDC's PWL system does is periodically perform one or more full strokes, in order to prevent the armature sticking in one place if the bulk of the disk operations are taking place in a few of the tracks on a drive.
I can kinda see the point, but to be honest I can't really see it being a huge benefit in practice. And it's all but irrelevant (IMO) for 'normal' consumer NASes, OS drives etc. An enterprise application where very little data is actually written on a drive compared to its capacity (ie high spindle count applications) could also benefit, and maybe some CCTV systems. But all in all not that useful.
Now I could be wrong - I haven't seen a whitepaper on the technology so I may be barking up the wrong tree entirely... :)