It probably comes as a surprise to discover that there are in fact, multiple types of switch plates available. There are actually a few technical differences that separate each type of switch and its necessary to understand them when choosing switch plates, so let's take a quick look at what they are.
Decora switch plates house a particular set of outlets or switches all designed to fit into the same opening, which is a rectangle approximately 2.5" in height by 1.25" in width. Normally, this opening is best suited for duplex power outlets, rocker switches and sliding dimmer switches.
The decora shape is standardized, which makes swapping out or installing devices and switches easier. The wide opening is also particularly useful in installing wide rocker switches, which are easier for elderly people to use.
Toggle switches are another extremely common switch type and look like a far narrower and smaller version of rocker or decora switches. These switches function identically to decora switches and are suitable for use at eye level.
Duplex devices have two receptacles or switches on a single electrical box or housing. Normally, this housing is "single gang", which refers to the width of the electrical box or switch plate. It is possible for duplex switches to be found in multi-gang arrangements but these tend to be bulky and best used in locations out of direct eyesight.
Dimmer switches are available as sliding, rocker, toggle and rotary switches that allow you to customize lighting in a room more than typical switches. Dimmer switches are a good fit for your A/V room or for creating ambiance in your dining or living room.