Swing arm rods attach to only one side of a window or door frame. Rods can be mounted singly to cover a whole window or in pairs so that opened curtains frame the window conventionally. Rods come in a variety of styles from antique to contemporary styles, as well as several sizes to accommodate different weights of fabric.
In general, light rods hold light fabrics and thicker rods hold heavier ones, although you may want to look more closely at weight capacities, especially if you are hanging a curtain at a doorway rather than a window.
Swing arm rods work well, singly or in pairs, in situations where opening windows might expose curtains to damage. Casement windows, for example, fully open out, exposing the curtain to weather, top to bottom. Being able to swing curtains away from the window may help prolong fabric life. Swing arms also address situations in which small or dormer windows provide enough light in a room only when uncovered. Rotate curtains away from the window during the day, then swing back to provide privacy at night.
Consider using swing arm curtain rods to curtain a sliding glass door. Especially in a climate that allows frequent use of patio or terrace doors, swing arm rods keep curtains from blowing outside or tangling with people entering or leaving. Curtains will stay cleaner and last longer if they do not need to be pulled away from the door repeatedly. Or use a swing arm rod effectively on interior doorways. In tight spaces, mount a swing arm rod to a storage closet, laundry alcove or even a guest bed as a divider.
For a shared bedroom or bathroom, consider mounting a swing arm curtain rod and creating a close to floor length partial room divider. Sisters sharing a room, for example, may appreciate privacy as well as the flexibility of space. Swing arm rods could also hold curtains to frame the couch when it functions as a guest bed. Conceal kitchen chaos from a small eating area when there's company at dinner. Weighting the hem of a swing arm-mounted curtain with a dowel will keep the curtain flat and a bit more wall-like. Use a swing arm to hold a beaded or creative curtain on your terrace.
The major aesthetic challenge with swing arm curtain rods is the appearance of the back of the curtain. Sheer curtains tend will look much the same. With heavier fabrics that have a definite face side, you may want to choose a lining that looks attractive when the curtain is swung back from the window. One solution is to double the fabric used, so that curtains look the same open or closed.