I am tending to use scientific names more and more. I like how their organized by how closely related they are. Within a family are fairly well related, withing a genus are more closely related, etc.
I generally stop at genus because I have a lot of trouble positively identifying species within a genus. I can take a good guess, but it's usually a guess, and ultimately not that important.
Within a genus, the various species may differ a little by size and color and time period. But on stream, I find that ID doesn't matter so much for those things. Those things vary from stream to stream anyway. So you still have to look at the bug and say "that's a size 16 yellow colored dun", then match it.
But the ID is more important for tactics. And for those, genus is usually enough. Bugs within a genus are typically the same as far as habits. Do the nymphs occupy fast, slow, silty, rocky areas? What water characteristics do they hatch from, or do they crawl to shore and do it there? Do nymphs transform to duns on the bottom or top? If top, do they float as nymphs for a while, or do it quickly? And once they're duns, do they ride the surface for a long time or get airborned quickly? Once airborne, what's the spinner behavior? Do they become spinners in an hour or two or a day or two? What time do they come back, morning, evening, overnight? Do they usually fall on water or land, and if water, over riffles?
These are important questions. And the differences between species within a genus is minor. The difference between genus's and families is often major.
BWO's is a great example. If they are Baetis, and the hatch is winding down, I'm sticking around, because the hatch comes in "waves", so they'll likely start up again, and spinners are largely unimportant anyway. If they are Drunella's, I'm probably gonna leave and get a bite to eat and come back tonight, because the hatch is over for today but I should expect a decent spinner fall tonight.
So, for instance, I wouldn't be too upset if you combined the common name March Brown and cahill. Different size and time period, but very similar bugs IMO, closely related in "habit". But I'd resist lumping Leucrocuta hebe in with either group.