Covers recommended?

[Bird]

The effect covers have on the sound of a pickup was answered by Tim in the "Common Ordering FAQ. But I was wondering, are there any pickups for which covers are recommened :?:

[Tim]

Covers are a great tonal shaping tool as they effectively shield the pickup and also lower the resonant peak slightly.The effect is off a slight warming of the tone and subtle rounding of the highs.
I voice certain pickups, like the Mule for instance, with a cover.If a customer wants the same tone but no cover/open coils then I adjust the wind to create the same effect.