I get where you're coming from - I work from home so almost all of my contexts are always available.
That said, I do still use contexts. Why? Because it makes it easy to batch similar tasks. If I've sat down at my computer and opened a specific program (perhaps web design software) then I might as well knock out the 4 other similar tasks from 3 other projects at the same time, while I'm in that 'mode' of thinking.
For me, there's no extra processing involved - if I haven't decided whether a task requires a phonecall or sitting down at my computer, then I clearly haven't finished clarifying the nature of the task.