My biggie is being able to lug around four wheels/tires without having to either make two trips or use both cars on the same trip.
The wheels/tires on the 1M are huge.
And while either of our e82s can take rear passengers (and rarely do), it does add some complexity when we go somewhere with my parents or I have to take one / both of them somewhere. There's no getting in the back for them...they're too old. This was where my V70R was perfect, and while my parents have an XC70, then there's car swapping involved.
I know...first-world problems.