Pianos are complex instruments with many sensitive parts. Action regulation is the process that adjusts the connection from the hammers to pedals, dampers and so on.
A new piano should be regulated after the first year. Manufacturers recommend regulation every four to five years thereafter.
While most piano owners know the importance of tuning, regulation may be forgotten. However, use of the instrument, time, temperature, humidity, and more effect a piano’s action, in turn affecting its touch and thus, the sound.
In the case that you experience a buzzing sound, sticking notes or uneven keys, your piano may be a candidate for regulation, or at least some attention.