Free vs. Refresh in ABAP
FREE- You can use FREE to initialize an internal table and release its memory space without first using the REFRESH or CLEAR statement. Like REFRESH, FREE works on the table body, not on the table work area. After a FREE statement, you can address the internal table again. It still occupies the amount of memory required for its header (currently 256 bytes). When you refill the table, the system has to allocate new memory space to the lines.
REFRESH- This always applies to the body of the table. As with the CLEAR statement, the memory used by the table before you initialized it remains allocated.