In my 30+ years of serious gigging, there have been 2 occasions when I could have done with a backup amp.
1993ish, my old Laney 4x10 combo blew a speaker. Spent the rest of the gig sounding like an elderly flatulent rhino.
Last year, my Shuttle 6 developed an intermittent cutting-out fault. Turned out that the preamp valve had worked its way partially out of the socket. Re-seated the valve, done.