Yes, it can be used without the discs. Without them, at large apertures you get pure spherical abberation causing the soft focus effect (which disappears as you stop down). This is sort of "Boudoir" photography, where you lose information due to spherical abberations. With the discs, you get the spherical abberation overlayed with image information that's out-of-register with the main image but that does have detail (sort of like adding a bunch of pinhole images over a main, soft image). Disc 3 has the most effect, but if the price is right you can get it without and shoot "boidoir" type stuff at large apertures and sharp pics at small apertures without the discs, as well as getting some of the normal "Soft Focus" effect the lens is famous for with the other 2 discs.
If the price is good, go for it. It's an amazing lens and it's hard to find on the used market. Even without disc 3 it's still a great piece of glass.
, but 150mm SF is not hard to find at all. Try Dead Link Removed if you are looking for one.