Dependent on the chosen aperture (f-stop),
the focal length and the focus distance you have a certain depth-of-field (DOF). The DOF defines a zone around the chosen focus point where objects
appear to be sharp. Beyond the (floating) border of this zone objects get
blurry. Typical beginners tend to think that a good picture is a picture
where everything is sharp so often small aperture values are preferred
in order to maximize the depth-of-field. This assumption works fine some
photographics scenes but it's certainly wrong as a general shooting philosophy.
All pictures provided by Michael Wagner.
The following picture (large aperture)
isolates a small zone around the focus plane.
The next picture (same focus plane) was shot with minimal aperture to achieve max. depth-of-field.
The next shot (large aperture) isolates
the foreground ...
... whereas this one prefers a different focus plane (same aperture).
As you can see we have lots of potential creativity just by selecting the aperture and focus plane.