Can tuning neglect damage a piano? Quotables.

"When tuning has been neglected for an extended period of time, the strings in the tenor, mid-range and extreme treble have often dropped in pitch much more, in comparison with the bass strings which have also dropped in pitch. The string tension has decreased so much and unevenly, that the soundboard and bridges have warped out of shape, placing tremendous strain on wood and glue joints, risking severe damage." 
  - Guus van den Braak, Registered Piano Technician (Australasian).

“…pianos are designed to be at a specific tension. When the tension is allowed to go flat the soundboard may flatten resulting in less downbearing on the strings and an increase in the chance of wild strings, cracks in the soundboard and case and frame parts separating."
 -  Cited from the Randy Potter School of Piano Technology, Inc. by  Randy Potter, Registered Piano Technician,  chapter 1.8 pg.16.   

"If the piano has fallen substantially below pitch (i.e. from not having been tuned frequently enough), the process of pulling the strings back up to pitch often brings these little bends out into the speaking segment of the string without having had the opportunity to straighten out gradually. A competent tuner can usually remove these unwanted bends in the string, but it's additional work, and you may get charged more. Some tuners who are not so competent just leave them and hope they'll straighten out over time. And sometimes, no matter how good the tuner is or how hard he tries to remove a false beat, you're stuck with it." 
- Piano Finders®


"Can the Piano Be Damaged by Not Having it Tuned?

"To keep a piano untuned for many years could do permanent damage to the piano. The strings are under a great deal of tension and tend to loose their tension over time. If the piano is kept untuned for too long you run the risk of the total pitch of the piano dropping. To bring the piano back to standard pitch may cause, at best, the necessity for several tunings over several weeks (at a higher cost) or, at worst, string breakage, and split bridges. Not only that, but playing on a poorly tuned piano can cause a potential musician to subconsciously not enjoy playing and hence, not wish to play."
  - Carl Radford, RPT


"Distortion in sound. In rare cases major tuning work can bring bends into the speaking length of the string causing distortion in the sound. Restringing is the only solution in this case." - Daniel Berg, RPT  excerpt from  Results from years of neglect.

"Take care of your piano by not neglecting it for extended periods of time.  Piano strings stretch over time, and if left untuned for long enough, a piano will require a major pitch raising when it is tuned again.  A major pitch raising is not good for the health of your piano; it increases the possibility of breaking some strings and/or may introduce a permanent out-of-tune sound known as 'false beating.' " - Gooch Piano Service
 

"The false beat is one of the tuner's worst enemies. This is a beat within a single string
that you can't eliminate by tuning. A string with a false beat sounds like two
strings that are out of tune with each other. False beats occur most commonly in the
upper middle register of the piano, from the treble break up to the middle of the top
octave.

"Other causes of false beats include rusty strings, kinked or twisted treble strings, and
strings that were stretched too much during stringing, pitch raising, or tuning. If you see
a kink or bend in the speaking portion of a string, try to straighten it by burnishing with
a steel rod. If this doesn't work, loosen the string and straighten it carefully with smooth
pliers. If it still sounds bad, replace it."  

- Piano Servicing, Tuning, and Rebuilding, 
Arthur A, Reblitz, RPT