Many beginner and intermediate pianists never use the top or bottom notes on a piano. Does it really matter if they are properly tuned? Shouldn’t you be able to save some money by having your tuner just skip those places until your child begins playing music that uses the extremes of the keyboard? Absolutely not!
Whenever a string on a piano sounds, we can hear not only the note played (the fundamental), but also many others (called harmonics). When the rest of the piano is in tune, strings not being played will vibrate slightly with the one(s) being played. This effect gives the piano a much richer and more pleasant tone. The piano sounds better when the entire instrument is in tune, even if some notes are never played!