Regardless of whether you have a 9ft Grand, or a Spinet, if the instrument is played regularly, it will require regular tuning.
1905 Schiller Upright. With proper care these old instruments outlive their owners!
Repair
Like any machine, over time parts wear out. A seemingly small problem with an action component could easily have a cascading effect that could damage other parts. It is important to have these parts repaired or replaced as soon as possible.
Regulation
A piano is like any other machine as it contains many moving and stationary parts that over time require adjustment. There are many of these adjustments per key. If the piano doesn't feel consistent up and down the keyboard, it will affect the way you play and the way a student learns. A regulation can solve these "touch problem" and to compensate for normal wear and tear.
Sometimes action work needs to be done outside of the piano.