It may be that you are one of the people who don't have much need for the context notion. There's nothing wrong with that, if it is true, but even people who are always in the same place with all of their resources at their fingertips can often get some value from contexts.
The most obvious use of the context idea is to separate out the tasks that can only be done in a given set of circumstances. For example, one might have a Calls or Phone context which would be assigned to actions like "Call gallery about new show". You can only act on those actions when you have a phone available. Another might be "Studio" for actions which can only be completed in the studio, or "Computer" for actions which can only be done on the computer. Those are what one might call hard-edged or physical contexts, because the definition what is or isn't in the context is easy to see. If you don't have a phone with you, you won't be making any phone calls!
Another potential use for the context notion is for what I think of as "virtual" contexts. These are classifications that don't have the same physical restrictions as the ones previously mentioned. These might be used for grouping your work to be more efficient. An example might be "Scanner" for things done on the scanner (which is attached to your computer, so it might go in the "Computer" context). Warming up the scanner, clearing the space around it, etc. all takes some time, so it would be nice to scan everything that has accumulated when you scan something instead of repeating the setup work over and over. So, when you sit down to scan something, you can see if there is other work you could profitably do in that "context" to amortize the warm up time over several items. Or you might set up such a context for online shopping, to help you group your purchases to save money on shipping.
I have a bunch of contexts for parts of my home -- garage, kitchen, office, etc. I can easily move between these contexts in a few seconds, so there isn't necessarily a huge time/effort savings by working in just one context at a time. Where the payoff comes is in deciding which areas might need more attention. I can fire up Curt Clifton's WhereToFocus
dashboard widget and pick one of the contexts that has the biggest pile of work to do. I find this useful for the large quantity of tasks I have which have no real time pressure but nonetheless need to be done on occasion.
For me, much of my work could be done without the traditional GTD context notion, but I find it more productive to use it in the somewhat more flexible ways suggested above.