Scale is about size, specifically relative size. It's best understood relative to people. Since we all know how big people are, generally speaking, a relationship can be easily determined. Scale can also reference the relative size of buildings, landscapes, and all types of objects. But the key to understanding scale is in the relationship to something known. This is perfectly illustrated in the 1977 short film "The Powers of Ten" Charles & Ray Eames (above). With it's single constant shot the film brings us through scale both large and small starting with the human scale (10 to the power of zero), the undeniable relationships at at each scale is presented.
Awareness and the consideration of scale when designing leads to better design. When our cities, buildings, public spaces, furnishings, hardware, etc., are "in scale", design intent becomes more clear. Thus, understanding scale leads to a better understanding of our surroundings; both natural and man made. This understanding, in turn, makes us better designers and, just as important, better critics of design. Better critics can more effectively demand, and get, a well designed society, which means more engagement, open dialog, and the free exchange of ideas, while ensuring the needs of the public at large are being served.
Granted, scale isn't the only thing that leads to good design but it is of fundamental importance. Sometimes we need a reminder, and it's important to get back to the basics. So, consider the scale of the places you visit. Find the relationships between the city plan, the building plan, and the detail. If the relationships aren't there or there is conflict, offer your critique, for all of our benefit.