It saves you the trouble of getting rid of the French fleet. That not only saves you one sub on average (or dd, depending what you send), it also frees up the Italian planes to do some other important stuff.
It gives you 3 free inf in North Africa, which is worth 9 IPC. And you don’t need to send a transport there, which you usually can’t defend.
It gives you the opportunity to land in TRJ or even Syria, really threatening Cairo and Iraq at the same time.
IPC-wise, it’s already a huge boost in the first 2-3 rounds. But more importantly, Italian units are very scarce at the beginning - but lots of stuff to do. Greece, Gibraltar, Malta, North Africa, Cairo, Syria, clearing the med - these are all goals Italy ideally wants to achieve within 3 turns. But that’s not really possible without Vichy, because you just can’t spread your units so much.
How often am I sacrificing a transport in the regular version, just to get Morocco for the bonus, for example…