Why would a plant like this spend a lot of water and energy to produce succulent leaves, only to let them die back when the dry period arrives?
The only reason I can think of is the following: in winter there is a surplus of water, which the woody underground tuber cannot absorb quickly enough.
Leaves, even succulent ones, can grow much faster than tubers, and therefore can store more water in a shorter period. When the weather starts becoming drier and hotter, the water in the leaves is then gradually absorbed by the tuber.
This recycling of water is best known from the mesemb family. It works a bit differently there (for one, very few Mesembs have tubers) but the general idea seems to me to be the same. For more info on this phenomenon, have a look at Water recycling in succulents.
B. succulenta is often locally abundant in the western part of the Little Karoo and further northwards (Tanqua Karoo and Bokkeveld Mts).
Although the leaves in this species may be up to 13 cm long, they are usually much shorter; the width varies from 0.3-1 cm.
The flowers appear from July through September and are yellow (as in nearly all Bulbines).
Pictures are in chronological order:
1 taken 11 July
2 and 3: 4 Sept.
4: 1 Oct.