I have never actually played the violin, but have looked at some of the techniques online. I was curious about it because violinists seem to play with so much confidence and effortless speed.
Of course, violinists practice for years, normally under a classical teacher. It's pretty much monophonic, with fiddle players being the exception, so they don't learn a lot of different chords on the instrument. They have the advantage (but also the challenge) of using a bow which makes everlasting sustain possible.
The bow also requires special fingering techniques when playing from higher to lower notes, in that the fingers need to be placed in preparation for the notes that will be played. Similar to a pull-off on the guitar, the higher notes give way to the lower notes as the bow is drawn across the string, but no pull-off happens. They lift the higher finger to expose the lower finger, all while the bow is generating continuous sound.
After this discovery, I tried to bring some of that fingering technique into playing guitar and believe it helped in playing single notes.
I then looked into how violinists look at the fingerboard. First, the standard tuning for the four strings goes up in fifths, with the notes G D A E. That's compared to the guitar's six strings tuned up in fourths, except for the G to B string being a major third. Second, violinists are taught to play in several positions along the length of the neck. The positions overlap and help with playing in tune on the fretless fingerboard. The violin's tuning and positions give it more consistency and predictability than the guitar.
It seems like some of that consistency could be brought over to the guitar. Except for special tunings, like drop-D and in slack key guitar, the guitar's tuning is pretty well set. In its standard tuning, the major third in the midst of the fourths will continue to require a one fret adjustment when playing from one side of the B string to the other. After all, we need the closer tuning between the G and B strings to help us make chords, and there are probably other reasons why it was settled on over the years.
As for positions on the guitar, making chord shapes is similar to positions, but that didn't seem (at first) to help me very much with playing single notes. After finding out about CAGED, and then the scales and chords that fit in the location of the CAGED chords, the next step was putting them all together and try to show them all on one diagram.
Not that I'm trying to turn guitar playing into violin playing. The violin positions are defined locations on the fingerboard. Different keys are played by changing fingerings in the positions.
On the guitar, the positions (my name for them after being unable to come up with a better one) are clusters of fingerings that are always in the same relative location to one another. The positions are moved along the neck to play in different keys. The fingerings always remain the same on every Fretboard Positions Diagram, in every key. With all of the scales, modes, chords, and intervals that can be understood and played with the fingerings in every position, I think that's pretty amazing!
The Fretboard Positions Diagram certainly isn't the answer to everything on the guitar. I'm sure it's been a tremendous help to me.