Normal shower bases have a smoothly sloped bowl shape to them which limits the size of the floor tile to four inches by four inches.
An envelope cut shower base allows you to have large tiles over 4 inches on the shower floor. This is because the envelope cut has four flat planes all pointing towards the drain.
There will be diagonal grout lines from the corners of the shower to the corners of the drain grate. These grout joints may become a design element, or can be minimized by using a tile colored grout just for those diagonal joints making them disappear.
Envelope cut shower bases still need to follow the required 2% to 4% slope rule as set by industry standards. Be sure to check the slope measurements by following the instructions in this video.
