Varying row sizes: ASSM is better than a static pctused. The bitmaps make ASSM tablespaces better at handling rows with wide variations in row length.
Reducing buffer busy waits: ASSM will remove buffer busy waits better than using multiple freelists. When a table has multiple freelists, all purges must be parallelized to reload the freelists evenly, and ASSM has no such limitation.
Great for Real Application Clusters: The bitmap freelists remove the need to define multiple freelists groups for RAC and provide overall improved freelist management over traditional freelists.