What are the advantages?

[Walrus]

Hi

A squad / unit can be rallied by itself, it's platoon commander, it's company commander and finally by the HQ.
If you attach independent platoons to company commanders, they gain an extra level of rally.
That's really the crux of it IMO.

Be careful not to attach too many ptns to any given commander.

I am sure others will have a more in depth answer.

Good luck
Walrus