Clean rock is often used for aesthetic purposes, when replacing turf, or mulch in making a ‘xeriscape’ (low water consumption) landscape. If you want to have large patches of space on your landscape that will not be walked on and won’t have turf, you’ll want to use crushed clean rock. Scatter some boulders, and some low-water native plants and you’ll have a proper xeriscaped space.
Clean rock is also used to surround drainage areas and for water filtration, as it still lets water flow through, but does effectively slow it down. Retention basins often used crushed clean rock.
Clean rock can also be used in conjunction with minus when building driveways. The clean is the bottom layer, to create stability, and then with minus rock as a top layer, to fill in all the cracks and provide a smoother driving surface. You can make a driveway with JUST the clean rock, but it might be a bit bumpy, and hard on your tires.
Minus can be used by itself for hiking trails and garden paths. These surfaces only need to bare the weight of foot traffic, so it is not essential that they are reinforced with large clean rocks as a foundation (but you certainly can if you want, it just costs more money but does end up lasting longer). Keep in mind, when using minus as a walkway, the dust on these will track on your shoes, therefore home owners should keep that in mind if using them in their backyard.