Landscaping is the design and care of the exterior of our buildings and homes. It includes deciding where to plant what, what other things to place outside (fountains, statues, fences, etc.). This exterior design also includes consideration of pathways, vistas, what fits with the style of the home and will create good window views.
Consider the look and maintenance.
Some plants will thrive more easily in certain environments than others. For instance, if you live in a dry climate, a rock garden or cactus garden may be easier and cheaper to maintain.
Perhaps some years you have more time to dedicate to the exterior of your home than others? So by planting things that will survive the winter, you can save yourself the effort of needing to replant annuals each year.
For trees and shrubs that can grow much larger over time, consider their full size in deciding where to place them. Tree roots can damage house foundations, pavement and other things. Constant abrasion by branches can damage the roof or exterior of your home.
Other reasons to use some plants is to create privacy by planting something in front of windows. Prickly plants in front of windows can also make it harder for someone to break-into a house. Plants can also be used to create borders or "separate spaces" -- either by creating a kind of hedge or fence, or by making different sections of the yard look different. For instance part of the yard could be formal and decorative with fancy flower bed borders, while other sections might be plainer and hold things like a children's play area.