Making a slit in the Stop Off Gassing, Mattress Wrap is highly suggested as it helps your mattress “breathe” to decrease chances of mold growth inside the mattress. It also allows the gases to slowly release, away from your lungs and skin. Gas generation happens in all mattresses, and gets worse as the mattress ages. Body heat & dampness from sweat or condensation causes mold growth; the mold eats components of the mattress; this action releases neuro-toxic gases (depending on what the mattress is made from).
Vent holes under or at the end of the bed, significantly reduce the harmful gases and keep them away from the person sleeping in the bed.
If you are not comfortable with this you can leave your mattress wrap intact, but you take on the possibility of increased fungal growth inside your mattress, and realize that you may experience “puffing up” under the wrap when you move around on the mattress.