I've recently found a channel on Youtube where a jet engine technician goes into great detail about the work he does on maintaining and repairing jet engines
In this particular video (and also an older prequel to it), he demonstrates removing nicks from compressor blade leading edges and subsequently smoothing out the leading edge. One thing that caught my attention was the tools he used: files and 100- and 400-grit sandpaper. He basically went over the leading edge by hand, removing a small amount of material in the process.
With the tools and the method, there is obviously no precision.
Is it actually acceptable to modify compressor blades that way? To what extent does it affect the operation and efficiency of the engine, if, say, some compressor blades are missing a millimetre off their chord, or have lost their twist by a few degrees?
I guess a related question is - what precision are compressor blades designed and built to?
Thanks to ymb1 for pointing out a related question, but I'm more interested in a quantification or analysis of the impact to the engine performance. It seems that the linked question explains the term blending (which is mentioned in the video as well), but did not go into details about performance impact.