Scans and scanlations have two, contrary effects on sales. On the one hand, some readers substitute scans for the option of purchase; on the other hand, some readers are made aware of the work by the scan or scanlation, and respond by purchasing it.
In the case of readers who cannot read the work in its original language, nor in a language into which a licensed translation has been made, the first effect basically does not hold at all; but, exposed to the work, they may agitate a publisher to produce a licensed translation in a language that they
can read.
As to
unforeseeable intentions, it's fairly obvious that, if a scanlation group had
intentions contrary to the expressed wishes of the creator, the group would just
ignore a request to stop.
As for me, I'll miss the comments by
@ShunZephyr and by
@Tsudow more than I'll miss the scanlation.