Black Point Compensation (BPC) applied twice to an image = shadow or colour issues?

Black point compensation is designed to avoid clipping of near black values. In your example of moving from a large document space to a smaller document space, then to an even smaller print space, leaving black compensation off at either conversion will result in near black values being clipped and, once clipped, they cannot be recovered in a later conversion. 

Dave

Right. BPC should in practice always be on.

Do you experience black clipping, or lifted blacks, somewhere? Then there are other reasons for it.

In almost all situations, you would want to enable BPC when using Relative Colorimetric rendering intent, especially when going from an RGB working/editing space to a printer profile. If using non-Adobe software that doesn't offer BPC, I would then use Perceptual rendering over Relative Colorimetric if there was any concern of losing shadow detail. In some very rare non-photographic situations which are very image specific, one may prefer to go from CMYK to RGB using Relative Colorimetric without BPC, however, this would be very rare. BPC generally helps more than it hurts, which is why it's there.