I may be wrong and this is just my opinion, but...comb filtering is the evil effect of poor mic technique, false and self-deceptive depth of field, and something to be avoided at all costs when making a record.

Just my opinion.

comb filtering can have a good effect on electronica vocals, and for some synths, so yes it does have a use, its just very experimental.

redrabbit wrote: Do I need to be carefull when adding additional processing/effects downstream of the filter ?.....to avoid problems resulting if the "new" stereo signal is ever summed back to mono (radio/tv broadcasts)....i.e. "apply additional processing/effects in equal amounts(???)......and e.q. upstream of the (comb) filter"

:roll:
the basic idea of these units is to have a mono signal that is near the same of the original signal ... pre effect.
This is an EQ and Level effect so any additional effect that is applied evenly to both left and right
should keep that mono compatability.

note:
it is almost impossible to answaer the above question without knowing the exact situation as there are many traps top fall into.
Some mix fellows would never use this sort of device and would probably look to other methods to widen an image.