Hi Kali. I would have thought most of us allow our orchids to grow bigger and so the probability of multiple spikes being high therefore a good chance of a magnificant display. Ofcourse due to the diversity of orchids about, there are miniatures and a huge variety of sizes inbetween and finally those that can be classified as big which may be unsuitable for a lot of growers due to space limitations. On a rough scale relating to adult sizes/bloom size from e.g 1 inch through to several feet and higher, height and width subject to the species itself.
Again if your concerned about space, plants can be divided as a means of propagation and possible sell, trade or gift leaving you with the plant but a smaller size and an opportunity to make room for a new orchid acquisition.
If your concerned with the space you have for orchid growin i.e a windowsill then a search on here or an engine would lead you to the max size a species/ hybrid will reach. However if you have a conservatory or greenhouse etc your options are greatly improved and your limitations reduced. The standard widely available Phalaenopsis hybrid (moth orchid) at adult size would not grow big and will tend to keep approx 4-6 leaves at all times, however its size is affected by the occurence of kekis (baby plants) and shoots which if kept together would obviously increase the overal size. By the time it has matured most would have taken measures to repot, divide and result in a more presentable tidy plant. Hope that helps a little.