*ramblings from the rabbitgeek*
A lot of people use Linebreeding to improve consistency in their bloodlines. That would be breeding father/daughter or mother/son, saving the best from those litters to breed back to the parent.
Inbreeding would be breeding brother/sister, which is another strategy that can be used sparingly to emphasize desired genetic traits like body type or color or markings. It can also emphasize negative traits so it must be used with a lot of caution and be prepared to remove any undesirable results immediately. Sometimes entire litters have to be culled.
Linebreeding can improve overall characteristics very quickly when careful selection of breeding stock is used. It can also bring a bloodline to a dead stop if one only focuses on looks and color. Selection for raising kits, fathering large litters, and having good survival rates of litters are also important production factors.
Linebreeding is also the way to establish a bloodline. By the third generation the rabbits are pretty much the result of the breeders selections and can be called their own bloodline, even if several breeders have their bloodline descended from the same source trio originally. Sometimes it is called a "closed herd" or closed bloodline because outside blood is rarely brought in.
Genetics is a lot like the dice game Yahtzee. You try to get sets of numbers to fill your scorecard. Sometimes you can "hold" or "fix" some of the variables by holding some dice before the next roll.
It can be amazing how many unseen genetic factors can be found when one keeps bringing in "outside blood" to avoid inbreeding.
Genetics can be like dealing poker hands. You take out (cull) the cards (genes) you don't want, shuffle the deck and deal again and soon you get the kind of combinations you want on a consistent basis.
Adding outside blood is like adding another deck of cards and trying to predict what combinations will occur. Then spend the next generations taking out the cards that are not wanted (selection). Trying to juggle the combinations from 5 or 6 different decks (bloodlines) can bring you to your knees, especially if something like white spots, bad teeth, or mismarked toenails become fixed in your herd.
Have a good day!