Synthetic hair extensions are used by many people for a number of reasons, some people just do not like the idea of wearing real hair and for many people it is the more affordable option costing on average one third less then the equivalent in real hair. Fake hair is made in almost every shade, curl and texture imaginable, and in myriad grades - from the cheapest doll hair to the best quality sort of hair you can wear 24 hours a day, 7 days a week, for months on end. The hair we use is made especially for us and is subjected to extra conditioning processes that result in its exceptional quality.
One of the reasons many people still enjoy the fake hair is that it does hold a style incredibly well; for example if you curl it with heated rollers the curl can last days instead of hours as it would with real hair, and if you want to wear it poker straight and have it stay that way, even in the rain, fake hair is possibly a better option. Another advantage is that you get more volume per connection then with real hair which is useful when being applied for thickness.
It is important to realise though, that there are also certain drawbacks in having fake hair such as you can not use heated styling equipment like straightening irons and curling tongs as these melt the hair so it does involve more aftercare to keep it looking really good.