Grasses can be used in both formal and informal landscape settings. Here is an excellent example of grasses being used in a “planned informality” setting.
The grasses add structure and texture as they soften the edges of the hardscape. Note how the grasses are used formally above the steps and more informally at the bottom of the picture.
Grasses are easy to work with, but they are not maintenance free. Being perennials, they have to be cut back every year to allow the newer fresher growth to come in. Also be be careful in the placement of the various varieties that are available. A small #01 pot can look cute when planted but you may find that it quickly grows to six feet tall.