If LASYNC= .TRUE. is set in the INCAR file, VASP will try to overlap communication with calculations. This switch is only supported in VASP.4.5 and newer releases, its use is however not recommended, since LASYNC=.TRUE. has not been tested carefully.
Overlapping communication and calculations, might improve performance a little bit, but it is also possible that the performance drops significantly. Please try yourself, and send a brief report to Georg.Kresse@univie.ac.at.