With few exceptions, plants dislike confinement of their roots. They prefer to be in the ground where they can disperse roots freely. Houseplants stay potted because of a lack of other soil inside. Some plants live in pots for portability. Some plants just happen to look good in pots. Plants in hanging planters conform to any combination of these and other reasons. They serve their purpose.
Most hanging planters are simple pots suspended by three wires, chains or strands of plastic, jointed at a hook or loop. The hook or loop hangs from a hook affixed to a ceiling, eave, rafter, beam or tree limb. Hanging baskets are pot-shaped mesh or metallic baskets outfitted with fibrous lining to contain the medium within. Small plants or cuttings can grow from holes cut through the lining.
Of course, hanging planters for houseplants are generally pots instead of baskets, which are too messy for inside. They are likely also outfitted with big saucers for drainage. Hanging planters just happen fit well into spaces that are not useful for much else, such as up near a ceiling in a corner. Many of the most popular houseplants just happen to cascade splendidly from hanging planters.
Portability is another advantage of potted plants. Hanging planters that contain frost sensitive plants outside can spend winter in sheltered situations. Orchids and epiphylums that are prominently displayed during bloom can return to less prominent spots when finished.
Hanging planters are popular mostly because some plants simply look better in them. Cascading houseplants like Boston fern, pothos and spider plant, might look a bit mundane on flat surfaces. Many low growing bedding plants are more impressive if suspended at eye level than they are in the ground. Some bedding plants and small perennials excel at cascading from hanging planters.
However, hanging planters are very different from the ground. Because of limited root dispersion, potted plants rely more on regular watering than those in the ground. Because they are exposed to open air, they dry out fast, so crave more water.
Tony Tomeo 
After I moved to Texas, I learned one more advantage of hanging plants. Favorites are far more easy to transport when it comes time to evacuate for a hurricane! (And, yes: that advice about watering was the first lesson I learned.)
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Oh my! I did not consider a hurricane. I think my houseplants would be on their own for that one. I would be SO gone.
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I toted two cacti with me for both Rita and Ike: their names were Godot (because I waited forever for him to bloom) and Godette, because she’s a bit of a floozy of a cactus that won’t stop blooming. Godot finally died, after about twenty years, but Godette’s still with me. She’s a columnar cactus that started out 4″ tall, and now she’s 2-1/2 ft. I’m hoping she’ll come back. I caught a squirrel sitting on top of her, and I suspect it damaged the top, where the flowers come out.
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Twenty years is impressive for a cactus. They are susceptible to rot as houseplants.
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The good news is that I live in Houston, and they had a patio with a hot, dry, and sunny N/NW exposure.
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So they were not full time houseplants.
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After buying pre-potted hanging plants at a nursery, I find it useful to remove them from the usually ugly plastic pot and repot them in nicer baskets, with better potting soil. The soil the nurseries use is often quite light and doesn’t retain moisture well. I water my hanging baskets every morning. If I mess up and one dries out too much, I take it down and plunk the whole thing in a large bowl of water. I let it sit there for a few hours and then hang it back up. 99 percent of the time, that revives it. One last thing–when we get rainy spells, it takes extra effort for me to remember that the hanging plants on one of my porches are well sheltered, and still need to be watered, despite the precipitation!
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Most houseplants are grown in medium that is designed for the nursery industry that grows them, with minimal concern for what happens to them beyond the nursery. They are considered to be disposable.
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