To dispel some apparent ignorance, both left and right hand dexterity is important for playing fretted string instruments, such as the guitar.
On the guitar, the left hand is doing a lot more than just pressing on strings: chords, slides, bends, tapping as in hammer-ons/pull-offs, natural harmonics, even muting strings in some techniques (see Stevie Ray Vaughan’s style).
The right hand is also doing more than just strumming or picking: two-handed tapping, artificial harmonics, palm muting, using the whammy bar to produce vibrato or whole-chord bends.
There are also techniques like sweep picking which require very precise coordination between both hands.
Same goes for fretless string instruments: playing long notes by drawing the bow over the strings (legato) is the bread and butter of bowed instruments like the violin and the cello, but they can also be played with short stabs of the bow (staccato) or by picking the strings with the fingers of the right hand (pizzicato), among others. Vibrato and slides are played using the left hand, simply by moving the finger up and down the string.
On the guitar, the left hand is doing a lot more than just pressing on strings: chords, slides, bends, tapping as in hammer-ons/pull-offs, natural harmonics, even muting strings in some techniques (see Stevie Ray Vaughan’s style).
The right hand is also doing more than just strumming or picking: two-handed tapping, artificial harmonics, palm muting, using the whammy bar to produce vibrato or whole-chord bends.
There are also techniques like sweep picking which require very precise coordination between both hands.
Same goes for fretless string instruments: playing long notes by drawing the bow over the strings (legato) is the bread and butter of bowed instruments like the violin and the cello, but they can also be played with short stabs of the bow (staccato) or by picking the strings with the fingers of the right hand (pizzicato), among others. Vibrato and slides are played using the left hand, simply by moving the finger up and down the string.