There are many reasons one may want to refret an instrument.  The most common is that the frets are too worn to level and dress them.  Another reason is to replace the frets with a different size wire that better suits the player’s style.  
 
     In some cases refrets are necessary to correct problems with a fingerboard. These problems sometime occur after a neck reset, but more often are dips and humps in the fingerboard.  Another common problem is necks that have too much relief for the truss rod to work correctly or guitars that have to much relief and have no adjustable truss rod such as an older Martin which has only a T shaped or hollow square reinforcement bar in the neck.  All of these problems can be corrected by planing the fingerboard after the frets are removed, usually using a neck jig so the guitar can be worked on as if it has string tension on the neck.
 
 
    Occasionally some guitars have “rubbery necks”. This term is used for guitar necks that lack the stiffness that most guitars have.  This problem can destroy the tone of
an instrument and make the truss rod work too hard.  In this case it would be wise to choose a fret wire with a bigger tang than some of the fret slots.  This form of compression fretting does a lot of good for a weak neck  by adding strength and tone back to the instrument.
    There are many different ways to install frets when a guitar is being refretted. The traditional way is with a hammer. Another way is with an arbor press or a hand held
press that squeezes the fret in (my personal favorite).  Next there is the glue in method.  This is where the fret slot is widened and the fret is glued in with epoxy.  I only use this method if it has already been done to the guitar in a previous refret.