Not as useful as a cresent wrench, too many times there won't be enough clearance for a box end.
Condo life means that sometimes I have to park my car about a block away, and today I walked down and found the battery dead, and a truck 4 feet in front of me so I couldn't start it with the clutch. I had a cheap copy of a leatherman and 12mm combo wrench in the car, which was good enough to get the cables off, but not the 5/16 bolt in the hold down. Gave me something to think about on the walk back to my garage.