Yeah, I understand your confusion, but yes it needs to cut through an opponent or simply through the Zanpakuto's release... the cuts are normal, but the area that is cuts is left barren of reiatsu... understand?!
For example, Rokuken comes to fight Byakuya and releases, Byakuya is immediately incapacitated to create any more reiatsu for his soul. Now, he releases Senbonzakura normaly, draining his leftover reiatsu not knowing of his sterility (let's say) and Senbonzakura's petals attack - If Rokuken slices through them it evaporates them since they are pure reishi, so Senbonzakura himself IS still capable of hurting Rokuken's wielder if the petals manage to come through to him, but if they are cut, they vanish. Also, if Rokuken slices Byakuya, the PART where it cuts is stripped of it's reiatsu... in time with multiple cuts it is drained more and more... the physical wounds can heal afterwards but in that place reiatsu will never exist again, leaving that place soul-less in a manner. If the opponent somehow manages to survive he can be filled with reiatsu in an artificial manner somehow, if someone gives it to him, but he himself won't ever be able to produce it again. Now, Zanpakuto are a different story, they are representations of other soul states of the Shinigami and a part of them but living as separate beings totally made of reishi, so if cut they are obliterated, not physically wounded because they don't have physical forms. This is quite a brutal way to cut someone off from his energy source, that is why Rokuken's attacks aren't more powerfull - their very core of action is absolute and incurable.
Since Zanpakuto's real forms are the blades, if a Zanpakuto's released form is cut it represents as the katana breaking pieces off itself... if a Zanpakuto is cut down to the end, the katana actually is shatters in pieces... if Rokuken slices through an unreleased Zanpakuto it cracks the reishi particles in it and breaks it - something like killing a Zanpakuto, the same goes for the wielders.
I hope this clarified things, sorry I wasn't more precise in the forementioned. :D
For example, Rokuken comes to fight Byakuya and releases, Byakuya is immediately incapacitated to create any more reiatsu for his soul. Now, he releases Senbonzakura normaly, draining his leftover reiatsu not knowing of his sterility (let's say) and Senbonzakura's petals attack - If Rokuken slices through them it evaporates them since they are pure reishi, so Senbonzakura himself IS still capable of hurting Rokuken's wielder if the petals manage to come through to him, but if they are cut, they vanish. Also, if Rokuken slices Byakuya, the PART where it cuts is stripped of it's reiatsu... in time with multiple cuts it is drained more and more... the physical wounds can heal afterwards but in that place reiatsu will never exist again, leaving that place soul-less in a manner. If the opponent somehow manages to survive he can be filled with reiatsu in an artificial manner somehow, if someone gives it to him, but he himself won't ever be able to produce it again. Now, Zanpakuto are a different story, they are representations of other soul states of the Shinigami and a part of them but living as separate beings totally made of reishi, so if cut they are obliterated, not physically wounded because they don't have physical forms. This is quite a brutal way to cut someone off from his energy source, that is why Rokuken's attacks aren't more powerfull - their very core of action is absolute and incurable.
Since Zanpakuto's real forms are the blades, if a Zanpakuto's released form is cut it represents as the katana breaking pieces off itself... if a Zanpakuto is cut down to the end, the katana actually is shatters in pieces... if Rokuken slices through an unreleased Zanpakuto it cracks the reishi particles in it and breaks it - something like killing a Zanpakuto, the same goes for the wielders.
I hope this clarified things, sorry I wasn't more precise in the forementioned. :D