If I have a particular gene in my herd that I want to solidify, I will breed two full siblings together without any second thoughts. As Pam mentioned, you can easily "pull out" the genes you WANT from doing full sibling crosses, but also due to the limited gene pool - don't be surprised if you find an undesirable gene or trait from such crosses as well.
The up side of a sibling cross producing undesirable genes or traits is that you know what lines carry what "unmentionables"... such as Malocclusion, Hydrocephalus, Split P, etc.
For instance... I have a REW doe and a Lilac buck, litter mates siredby a GC REW and a petite Chocolate doe who threw awesome fur on her offspring. Genetically, I know the REW doe is either a Chocolate or Lilac. I have bred the two siblings for the purpose of solidifying and "doubling up" the traits that their parents carriedas I unfortunately no longer have the parents. I want a buck and doe each (hopefully) that has the Type and Density of coat that their sire hadPLUS the Even and Nicely Finished texture that their Dam consistently produced. If I can "fuse" in those 2 traits into the same rabbit... WOW! And in this case,itcan only be accomplished by the full sibling cross.
Another example is two Lynx siblings... the buck I KNOW is (AabbC_ddEEww) and the doe is known to be (AabbCcddEE Dwdw). Their type compliments each other quite well... The doe has the definition in ring bands that I am breeding for, however the buck has the rufus coloring that I need to solidify in my herd. I'm hoping by doing this cross I can get a good meeting of both qualities... the only drawback I can see at this point is the dam of these two is known to carry the gene for Hydrocephalus. On the upside... if this crossing does NOT yield any kits with Hydrocephalus, then the odds are pretty good that it was not passed on by the dam. So, there are basically 2 key points FOR doing this cross.
Dr. Stephen Roush wrote something about linebreeding/inbreeding and how it's interpreted in different species (Dog, Rabbit, Human) - I actually found it quite informative and fascinating. I'll ask to see if I can quote him.
~Sunshine