Why would a customer want to change the cutting edge angle?
This procedure can be beneficial if the sharpened tool needs to have acute angle that will not require as much pressure when cutting. Albeit it changes the dexterity of the cutting edge as a whole, it improves the cutting accuracy. Kitchen knives is a common example of a tool that often need a new cutting edge angle post manufacturing.
But how about other tools? Depending on the purpose. Some tools require a precise angle to be able to cut. A good example is drill bits. If you sharpen a drill bit free hand, you risk of getting uneven wear of the cutting edge, resulting it to get misaligned in relation to the centre of the drill bit. If both cutting edges are not meeting at the centre, the drill bit will wobble, causing the hole to be bigger than needed. This would not work for a project with high tolerance requirements.