INITTRANS makes sense of course, but what is the other & why?

A. PCTUSED
B. PCTFREE
C. INITRANS
D. MAXEXTENTS
E. NEXTEXTENT

Good question. If you set a high value for PCTUSED, then you may decrease performance, because more migrated and
chained rows are present. Then low INITRANS on the other blocks may affect concurrency of the transaction.

With a low value for PCTUSED, the space usage is not efficient due to unused space in data blocks.