Scale often comes into play when one has to decide about a tree planting near a home. Take the yard in the photo above, for example. The tree (a dogwood tree) planted here can be said to be "in scale" with the house. Being a one-storey house, it is complemented best by a relatively short tree. A much larger tree would dwarf this home.
But scale can also come into play when planning foundation plantings -- specifically, in plant selection for the corners in a foundation planting. Corner plantings should be taller than the rest. Let scale be your guide, adjusting allowable plant height according to the height of your house.
However, sometimes you'll want to tweak the scale, so as to correct what you might view as a "fault" in the architecture. For instance, perhaps you feel that your ranch-style home gives too "horizontal" an impression. To correct this, plant something tall and skinny at each corner, such as Emerald Green arborvitae trees. Such corner plantings will break up the home's horizontality and lead the eye upwards.
By contrast, it is the verticality of the corners that you may wish to combat with a house that is relatively tall, compared to its width. In this case, a small tree with a horizontal branching habit can soften the home's vertical lines.