There are many reasons why you may want or need to adjust the string action of your Instrument. One obvious one is that you just don't like the action the guitar is set at, the frets, bridge, the nut have been replaced, or if you've recently changed string gauge. The change in the string tension because of the higher gage strings, will exerted more force on the neck and, in most cases, will have an effect on the neck relief.
There are several factors that need to be considered when adjusting the string action on your instrument, the fingerboard radius, neck relief, string gauge fret wear, fret size, bridge saddle, and the nut height.
All of the factors listed need to be carefully assessed before considering adjusting the string action. Replacing or changing any of these items will most likely change the string action. Of course changing or replacing any of these items necessitates the need to examine all of the items specifications before reseting the string action.
For example, string gage changes will cause more stress on the the neck causing the neck relief to change causing the the string action to change.
String action is directly effected by any changes to the nut, neck relief, bridge, or frets. So if any these need to be replaced or adjusted a thorough examination of all the specs need to be considered.
There are no set rules or specifications for string action it's up to the player to know how they want the instrument to play. There are factory specifications that is usually a good place to start from. While benchmark measurements help to put you in the ballpark for a good set up there are differences in each instrument which will factor into an ideal set up.
