Texturing aids mixing. Some say the texture holds some fuel/oil against its surface, and that a little bit more oil drips into the main bearings on account of it. Others say it stops "dry spots" within the crankcase. These super-smooth areas are created when a case is cast and cause an unsteady flow pattern to emerge. It's why like-kind engines report different flow and power numbers. Texturing evens the playing field. It's not the kind of thing I'd take an engine apart to do but I always recommend that it be done when the cases are coming apart anyway. It's an all gain - no pain modification that helps the bottom/mid range more than anywhere else in the power range, but it's just as "at home" inside a top end screamer. It's a "must-do" to any racing engine though.