Rock Slide and Brick Break are better in my opinion. Subpunching may not work well all the time.
Your opponent is using Exeggutor.
You are using Heracross.
Your opponent knows you have Megahorn.
Your opponent switches Exeggutor to save it for later use.
Your opponent switches in Skarmory.
You use Substitute.
Heracross tightens its focus.
Skarmory uses Drill Peck.
Heracross's Substitute breaks.
Heracross uses Focus Punch.
Skarmory is down by around 37-47% health.
You use Milotic.
Your opponent is using Camerupt.
Your opponent is not a fool.
You know this.
Your opponent switches out Camerupt.
Your opponent switches in Snorlax.
Milotic uses Hypnosis.
Snorlax falls asleep.
You switch in Heracross.
Snorlax is still asleep.
Your opponent switches out Snorlax.
Your opponent switches in Skarmory.
You use Substitute.
Heracross tightens its focus.
Skarmory uses Drill Peck.
Heracross's Substitute breaks.
Heracross uses Focus Punch.
Skarmory is down by around 37-47% health.
I've got about 50 more.