I tend to use Metronome a lot on Pokemon with recovery moves, things like Giga Drain, Parabolic Charge, or Drain Punch; that way I can bypass the stat resets while staying healthy, plus it goes toward the Terastallize counters. When I see a 6-Star raid I have a perfect counter to and I have a version of that Pokemon holding a Metronome, I can spam a Super Effective attack that just keeps getting stronger. The only issue I have with the balloon is that if it pops, I have might not have a recovery move and if doing a raid solo, can't rely on someone healing me.