This is a quick method of length reassignment surgery.
It lets you split off fabric very quickly and accurately, along an single row, and does not affect the live loops--the tugging to get the snipped yarn loose looks like it would distort the underlying fabric, but in all the years I have been doing this, the live loops are always in perfect shape once the tugging ends. You do lose the amount of yarn in one row, but this seems a small price to pay for not having to sit and squint at the fabric to unpick the snipped row.
Good knitting--TK