From Redrawing the Lines (just a site I found with a quick Google search, no special reason to pick it other than it is what I found):
Are states permitted to create new majority- minority districts?
States are permitted and sometimes required to create new majority-minority districts under the Voting Rights Act to avoid diluting minority voting strength during redistricting. States with significant minority population growth over the course of the last decade, for instance, may need to create new majority-minority districts to ensure that redistricting plans comply with the requirements of Section 2 of the Act. Plans that dilute minority voting strength by failing to create feasible majority-minority districts may be quickly challenged following adoption. Since Section 2 litigation can be both costly and time- consuming, officials in many states set out to draw plans that fairly reflect minority voting strength at the beginning of the redistricting process. The need to comply with Section 2 of the Voting Rights Act to avoid minority vote dilution can serve as a compelling justification for both preserving and creating new majority-minority districts, which helps protect these districts from constitutional attack.
From Cornell University, we have:
Section 2 of the VRA, codified at 42 U.S.C. 1973, prohibits drawing election districts in ways that improperly dilute minorities’ voting power. This prohibition applies to states, counties, cities, school districts, and any other governmental unit that holds elections. Two typical forms of vote dilution involve “cracking” a minority community between several election districts, and “submerging” minority communities in multi-member districts. Cracking occurs when election officials split a single minority community into enough different election districts that even if the community voted as a bloc, it could not influence any single districts’ elections. Alternately, election officials might dilute a minority community’s voting power by submerging it in a multi-member district with enough non-minority voters to routinely defeat the minority community’s chosen candidates. See Gerrymandering.
Personally, I find it all to be a bunch of bullcrap. Have you seen those voting districts that are along, squiggly lines that wander all over the place? Give me big squares, randomly generated with approval from a set of judges or something like that, and get the god damned legislators out of the district drawing business. I don't care who it "hurts" or "helps", it is ridiculous to have some of the districts that we do.