Well that all depends. As an installer. If we can get to the back of the carpet, we'll use an iron to break the seam and it generally it will go back together just find.... However I imagine in the a WD situation, the seam tape is going to be wet for the most part and that option goes out the window. If its a good seam and its been sealed with thermoplactic, you may ruin the chance for putting it back together with out problems by face cutting it. Doorways seams don't give you many options but to face cut it. Of course anytime you can avoid cutting a seam, you are better off. If you have to cut it from the face then your prescribed method above is just fine. If you can use a row finder and a rowcutter, also known as a cushion back cutter, you'll produce a better edge. This is beneficial because when the tape is dry, the installer can come back and melt the tape off with his iron, re seal the edge and seam it back together. But each situation is very unique depending on the room layout, registers in the floor, and placement of seams.