It is interesting how many uses one can come up with for a basic pair of glasses. Make those safety glasses, and the uses increase. Prescription safety glasses are arguably just about as useful as it can get, as they provide not only the ability to see but make life much safer for the person wearing them. After all, one of the problems with normal safety glasses is that they are usually close enough to the eyes that another pair of glasses cannot be worn underneath them; these glasses eschew that situation.
On a decidedly practical side, several occupations require the use of these types of glasses. Besides the aforementioned limited space issue, wearing glasses inside another pair can create several problems when it comes to seeing through the combined lenses. Also, wearers can suffer from increased humidity, making the glasses uncomfortable to wear. Because of this, those that must wear protective goggles for a long period usually opt for a prescription version.
This means that a wide number of occupations do better with prescription safety goggles. A medical researcher is no longer required to constantly remove his glasses to check slides. A chemist has a definite advantage, as he is now unlikely to forget to put on safety goggles if they are his normal set. Even a hardware specialist, who is required to wear goggles due to the potential of electrical shocks, can safely do his job.
Of course, there are some areas where having fun and wearing glasses is part of the fun. For those into extreme sports, for example, having an additional pair of glasses can make life difficult. There is an additional safety issue as well, as there are reasons that glasses for extreme sports enthusiasts tend to be lightweight, something that is difficult when you need to wear two sets of glasses at once. Crashes have been caused by less.
There are even hobbies where a set of prescription safety glasses can come in handy. For example, amateur brewers sometimes deal in some recipes involving heated rocks. The rocks glow and may break apart violently. Even for more normal recipes, having an additional layer of protection while you record the brewing is always nice.
Regardless of the reason that you wear prescription safety glasses, they do tend to be a bit more expensive than normal glasses. Most insurance does cover them, even though it may take some discussion, so they are not that hard to obtain. Just remember to take care of them, and they will do you in good stead.