As350 Mtow
The higher external load weight limitation is purely because the load is jettisonable.
As the load is slung directly below the rotor shaft there is no C of G issue.
As with any helicopter, if you operate at or in exceedance of the limit the machine may well still drag itself around the sky but should an Auto be required the aircraft will perform like a brick.
Its purely a concession which says that (as long as performance allows) you can use a helicopter (with ops normal) up to this limit, as long as and only if the additional allowance is but a push of a button away.