While HiRISE has imaged slope streaks before, bright streaks are not as common as dark ones, so they're of high interest.
Slope streaks are generally small features, and have an interior roughness that is finer than the width of the streak itself. A high resolution image can help identify the characteristics of this roughness.
Additionally, studying these streaks can shed light on the "life cycle" of a streak and the geologic processes that created them. We may also be able to study the photometric properties of the streaks.
(Note: the above image is not map-projected, so north is approximate down).
Photo credit: NASA/JPL/University of Arizona