Pianos are wonderful machines, and like all machines, they performed best when they are well maintained!
A yearly tuning will maintain your piano's pitch, but seasonal changes and frequent use often make your piano want a tuning every six months. Clubs, studios and churches often need much more frequent service, and a piano in a performance venue can be tuned three times a day, for rehearsal, soundcheck, and performance. Pianos that have languished without tuning for too long require extra maintenance to be brought up to speed, and the instrument's quality can be permanently affected.
As your piano matures, you will notice a difference in it's tone; hammers harden as they pack down, hitting the strings, and that harder hammer produces a brighter sound. A piano with overly soft hammers will often lack clarity of tone. Changing the consistency of a hammer can alter and refine you piano's tone. Voicing is a matter of taste, but your piano's tone can be modified to suit yours.