The radial tool is good to speed up from making 4 different gradients . . .
In addition to the above, you can have them "off center" it so that the resulting vignette-effect brings focus to a specific area of the image. Much harder to do "smoothly" w/ multiple linears. There are lots of other uses for large radial gradients as well, e.g. warmer to cooler, sharper to softer, etc.
But what I've found especially useful is using small radial gradients, with them "inverted. " This ends up working a lot like the "control points" in NIK applications. I've found it faster in some instances than using an adjustment brush - and especially nice with the ability to feather the effect(s). The ability to duplicate and then move any given small RG, and then tweak the size/settings is also very slick, IMO.
I'm a very happy camper w/ the Version 5 upgrade. The RG and the enhanced lens correction/upright feature were worth the price of admission.