Although not generally regarded as a structural element of a property, the ceiling conceals the underside of the floor and the roof structure. It is something that is often overlooked when planning the renovation of a room. Of course, ceilings are more complex than you might imagine; if you own a period house it may be listed in which case you may have to use unorthodox materials such as horse-hair in the plaster as was done at the time of original construction. Modern homes usually have featureless, flat surfaces and so only really require re-plastering, but older ones, especially those of Victorian construction are often have features such as complex cornices, roses around light fittings, etc.
Ceilings are the least considered of all the surfaces in a house. Originally they were constructed to reduce draughts and to hide the uglier features of a house such as the slat-work now replaced in modern homes by plasterboard. Nowadays they hide much more; false ceilings help cover up a multitude of sins such as cabling for electricity, networking, or air conditioning ducts and access tunnels. If a room has a picture rail, it is a good idea to paint the area above it, including the ceiling, a lighter shade of the wall covering or even using a contrasting, lighter colour. This has the effect of brightening up the room.
Most people live in houses where ceilings offer little in the way of value to the overall appearance, modern homes especially because of their boxy construction. Adding cornicing can reduce the harsh, functional appearance of the ceiling. If you are keen on gadgets and this particular room cries out for technology, say, for a study, a kitchen or a living room, then by adding a false ceiling cabling can be added easily to support the modern features you need around a house. Often a ceiling requires renovation because of the presence of Artex, a hard-wearing yet easy to apply substance mostly used to cover up a poor surface. Today it is outmoded and problematic as it also collects dust and grime over the years and so this becomes the number one reason for renovation of a ceiling.
Ceilings are the last place you want to renovate as a DIY challenge. Plastering is not something I would tackle for two reasons. The first is working upside down or with your neck at a strange angle for long periods of time will almost certainly require you to consider the extra cost of physiotherapy, and the second is that small imperfections will stand out in relief because of the shallow angle of the ceiling lights relative to this surface. Another good reason for employing a contractor is the need to ensure ceiling materials remain on the ceiling. Collapsing plaster work is heavy and could seriously injure anyone under it, especially small children. Skimming to remove the evidence of Artex is a skilled job, and unless you have this particular skill it is more likely you will make it look worse than it did at the beginning of the exercise.