The main problem is that the pattern of the full beam is not very good.
I have a Rockster, with the same headlight units as the 115GS, and while the dip-beam pattern is excellent, with a good kick up on the left (or right, it's adjustable), the full beam only fills about metre diameter circle at 75yards with light. So as soon as you tip into a fast bend at night, especially a right hander, you're blind because the road surface you're heading for is now above the pattern of light thrown by the full beam, and thus unlit.
My first solution (and the best I've used) was a pair of PIAA 1100X spots, which have a nice circular pattern, aimed to the left and right of the main beam, and slightly higher. They worked very well indeed.
I now have a pair of Hella FF50s, which are actually fog lights, and thus have a flat oval pattern, aimed somewhat similarly. They're not quite as good as the PIAAs, but they were a lot cheaper!
Obviously there's masses of auxiliary light options available, and everyone has different ideas about how to mount them or aim them. I personally always have them wired up so that they're only lit when the full beam comes on (I use a relay powered off the full-beam indicator light circuit), I don't see the need for having them on permanently (but again, that's just an opinion.
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