From the man page:
DESCRIPTION
This manual page documents briefly the partprobe command.partprobe is a program that informs the operating system kernel of partition table changes, by requesting that the operating system re-read the partition table.
Quite handy if you have shared storage connected to two or more cluster nodes (like an Oracle RAC) and you want, after creating partitions on the first node, to make the new partitions visible on the other nodes without a reboot.