Sanding Beam Butchery.
Logical thinking:
Frets are not flat, they are a compound radius, a radius that goes the fret length with the fretboard radius and the radius that forms the crown.
Sanding beams are flat. Commonsense tells you that the beam must sand the frets flat, destroying the fret crown.
Almost all fretboards have a radius that a flat beam cannot miraculoulsy form to, and so what happens, the fret radius is sanded uneven, butchering the radius.
Basic geometry says that if the fret radius does not perfectly match the fretboard radius which means the height across the fret must be consistently the same, there is no way the fret is level hence there is no way the frets can collectively be level.
It gets worse, much worse: A flat beam cannot self-adjust to the highs and lows of uneven (out of level) frets, and yet it is because of uneven frets that we are leveling the frets. It's a trap. The beam must rest on two points, must. When as is always the case with uneven frets, one of those two points is higher than the other so that the beam is not parallel level to the fretboard, it is at an angle, hence it must sand the frets on that angle.
Do you see the problem? Sanding frets at an angle means the result must be that the frets run from low to high, high to low. That is not level, that may be coplanar because a plane can be at any angle, but definitely not level unless it meets the definition of level ie; parallel to a reference horizon plane, in this case the fretboard.
Simple geometry, simple logic, it does not matter what the snake oil selling YouTubers pontificate to the contrary, they either do not know simple geometry, or they are just blowing gas to generate content for monetary gain, either way they are proliferating wrong information.
Prove it for yourself, use a digital gauge to measure your frets, you will be shocked at how messed up they are even after you just paid a shop to level them. It will become clear to you why your string action is higher than you like and why the neck relief compounds that issue.
Watch the video, witness in deep dive detail all the ways that using a sanding beam trashes the frets and the play and sound of the guitar at the same time.
Knowledge is freedom and power:
You have a real choice to never again pay a shop for fret leveling, to never again get the Jesse James screws put to you.