Programming challenge: wildcard exclusion in cartesian products

[funkyj]

wkehowski at cox.net wrote:
> It would seem that your program is just filtering the full cartesian
> product, right? The solution I'm looking for generates the elements
> one-by-one so that it could be used in a loop.

One advantage of a generator over filtering the full product is that I,
as the user of the generator, am not obligated to iterate over the
entire solution space.

Are there other _practical_ advantages of generators over mapping &
filtering complete sets?