You can use free space reallocation with the other reallocation features that you use to manage system performance: reallocation scans and read reallocation. However, you should not run an aggregate reallocation scan (reallocate -A) if free space reallocation is enabled on the aggregate.
When you enable free space reallocation, you should also consider enabling read reallocation. Free space reallocation and read reallocation are complimentary technologies that optimize data layout. Read reallocation optimizes the system for sequential reads, while free space reallocation optimizes for writes.