Pianos deserve to be tuned regularly, and the frequency of service will depend on their condition and use.

Leaving them alone for too long can cause problems, one of which is rust build up, resulting in broken strings.

There are literally hundreds of interrelated parts that are subject to wear in a piano, and it is best to keep them in good shape, so I always include Minor Action Adjustments in a Tuning Service and will advise you of, and quote, if there is more time consuming work due.