там к слову бенефиты расписаны:
if the CPU supports AVX or AVX2, use the 32-byte YMM registers for faster memory copy, and if the CPU supports AVX-512, use the 64-byte ZMM registers for even faster memory copy; use DisableAVX to turn AVX off completely or use DisableAVX1/DisableAVX2/DisableAVX512 to disable separately certain AVX-related instruction set from being compiled into FastMM4);
if EnableAVX is defined, all memory blocks are aligned by 32 bytes, but you can also use Align32Bytes define without AVX; please note that the memory overhead is higher when the blocks are aligned by 32 bytes, because some memory is lost by padding;
with AVX, memory copy is secure - all XMM/YMM/ZMM registers used to copy memory are cleared by vxorps/vpxor, so the leftovers of the copied memory are not exposed in the XMM/YMM/ZMM registers;
и так далее
ну и вишенка:
support for Lazarus 1.6.4 with FreePascal (the original FastMM4 4.992 requires modifications, it doesn't work under Lazarus 1.6.4 with FreePascal out-of-the-box, also tested under Lazarus 1.8.2 / FPC 3.0.4 with Win32 target;