I got asked an interesting question recently. It's a general rule of thumb that most landscape shots are made with the lens stopped way down to maximize depth of field. Given this, why would you need a lens with an f/2.8 aperture?
To answer this, let's fist look at that rule of thumb. Ansel Adams and other photographers in love with the American West popularized the very idea of landscape photography in order to capture the grand vistas they saw. Since grand vistas call for extreme depth of field in order to do justice to objects both far away and close up at the same time, small apertures were required. The large format cameras of the day often could be stopped down as far as f/64 which became the basis for the legendary F64 Club whose members including Adams insisted on tack sharp images shot at that small aperture.
Over time, film formats shrunk into the 35mm standard which formed the basic size reference for digital as well and f/64 simply wasn't practical in these mediums due to the effects of diffraction. While some lenses will go as small as f/32 (or rarely even smaller), most stop at f/22. Working at f/22 today is quite common for landscape work for the same reasons that Ansel Adams generally used the smallest aperture he had in his day. Big vistas require small apertures and the biggest vistas generally get shot at the smallest apertures available .
But not always. Sometimes you may only need to stop down partway to get everything sharp. With film, many photographers routinely stopped all the way down just to be safe but with digital you can find out whether you've truly nailed a shot before you get home. After reviewing the results, if you need more depth of field you can make the needed adjustments and fire off another shot while you're still there on location. This gives today's photographer enough confidence to explore more than just f/22, and since lenses tend to give their best results at less extreme f/stops there's a definite incentive to resort to f/22 only when truly necessary.
Digital also allows for a greater degree of experimentation for those willing to play with shallow depths of field and selective focus. If the out of focus portions of an image help to lead the eye to what the photographer's main interest was when taking a shot, wider apertures can become part of the creative process not a hindrance to it. As with most things, it is possible to overdo soft focus, but I have seen some excellent results come from employing fairly wide apertures on subjects that could still be considered landscapes.
This still leaves us rarely shooting wide open though. But what modern cameras always do wide open is focus. No matter how likely I may be to stop down in order to actually take a shot, both my camera and I appreciate the light gathering power of wide apertures when trying to focus before shooting. Composition works much better when I can actually see my subject too, and I regularly shoot landscape shots at the very edge of dawn or dusk when light is low.
For me, an f/2.8 maximum aperture is more than just a badge designating a lens as being "professional." It means it's a tool that I can use when effectively when many the best shots are even possible. After hiking more than a few miles up hill before sunrise with a pack loaded with f/2.8 lenses I do wish such lenses they weighed a bit less, but I'm willing to put in a bit of extra effort if the images that result reflect that.