For most of us, even those of us who work at home, a typical project will not consist solely of actions in a single context. I have contexts for each of the major "locations" in my home (garage, office, kitchen, laundry, etc.) as well as the various computers. I could lump everything into one colossal "home" context, certainly, but then I'd spend a lot more time looking at my lists trying to figure out what other things I needed to do on my iMac besides the daily backup, or searching for all the calls that I needed to make during business hours, and just what was that other thing that I needed to scan the next time I fire up the scanner? Similarly, a list of stuff to be done "on a computer" doesn't do me much good when most of it needs to be done (or is most conveniently done) on a specific computer (the one that has the iTunes library, or the Aperture library, the one that runs that other operating system). And what about those times when a project is paused waiting for something to happen? I've got Waiting contexts for my usual things I might wait on (mail, email, calls) and Agenda contexts for the people I interact with most frequently. When I speak to Fred next, I can be sure that we cover all of the topics we need to discuss by checking Agenda : Fred instead of searching through all the projects where Fred might conceivably play a role as I would have to do, if I had everything in the same context.
There's nothing intrinsically wrong with using a next action view in project mode to decide what to do next. The point of OmniFocus (and GTD) is to make it easier for you to make informed decisions about what you should do next.
There are a few things that do not work as well in project mode as in context mode. One of them is grouping by start or due date. The grouping will happen by the start or due date of the
project, not the actions contained therein. Single-action lists will get grouped by the start or due date of the single-action list, which is not very useful for my "miscellaneous" list! Doesn't matter if there are any actions in the project that are actually available to work on at the moment, if the project start date was last week, the project will show up in the Started last week group.
There's a trap for the unwary in your preferred work style (project view, selecting next action). Consider the following:
Let's look at that in your fashion:
Absolutely no indication that there's a later action in that project that is due today! Bad news if you don't happen to work on that project, no?
Now, it's a bit better if you happened to group by due:
We at least see that there is something in that project due today, though we don't see what it is.
Now, I can hear you saying "but if I did a context view, next actions only, I wouldn't see the about to be overdue action either, because it isn't a next action!" and I would certainly agree. But let's take a slightly different approach to the issue: what's the most efficient way to make sure that everything that is due today gets done today? Obviously, you could simply do everything, and that would be a splendid brute force solution. Feel free to swing by my place to help me out with some of my work when you're done with yours :-) Probably that's not really an option, so you need to pick and choose what you'll work on. If you do a context view, grouped by due, with remaining actions (or better yet, due soon, an option not provided in project mode) shown instead of next actions, you'll be able to see all of those items falling due today (or in the next few days), even if they aren't a next action at the moment. A view in project mode that will let you scan for upcoming due actions (as opposed to projects, I hope you agree there is an important difference!) will show you a huge amount of stuff that may not have any due date at all, leaving you to scan through every line looking for the items that are due soon. To be fair, in a case like the one I gave, where there's a due item later in a sequence after some actions that do not have explicit due dates, it might well be more convenient to stay in project mode banging away on the next actions until that project no longer shows up in the "due today" group.
To address your specific example, had you selected the group of projects you wanted to work on (to the exclusion of all else), clicked on the focus button (if you've installed it in your toolbar) or used the popup menu (ctrl-click in the sidebar, select Focus), you could have then switched to context mode and only seen the items from those projects, sorted into their respective contexts.