Over time, piano keys become out of level with each other, unevenly spaced, and tilted from side to side (out of square). This can cause the pianist some problems when trying to achieve uniformity of sound because the uniformity of touch is not present. It also looks bad from an aesthetic perspective.
To correct this, the keys can be leveled, properly spaced, and squared. This is best done in conjunction with regulating the complete action. However, if there are just a few problematic keys, then they can be addressed on their own without regulating the entire action. In fact, there have been instances where I have been called upon to repair some keys that were out of level only to find that foreign objects in the action were to blame. So, in some cases a proper cleaning will resolve leveling issues.
If you live in the Boise, Idaho region and have a piano in need of regulation, repair, or cleaning, contact me.