My understanding is that when you do a male/female cross from a strain, each has the variables from the parent plants, in full, and as such, the offspring possess the full potential of each. This can be controlled through selective culling. Eventually desired traits become dominant.
When using a herm'd clone on itself, the available genetic differences are from a single side of the equation. So the variances that the male would have had are not present. The possible outcomes of the fem will express, as well as possible mutations, but it's drawing from ua smaller pool. Especially considering how often people use the same male on lots of stuff, it seems you'd be more likely to get the pheno you'd like?.