Optimal Cutting is an Inquisition perk from Leilana (Secrets category). It says it Grants a 10% chance to receive extra herbs with each harvest.
I tried picking it up and see what it does.
I farmed the elfroot nursery on Emprise Du Lion near the starting camp, which has around 18 elfroot herbs.
What this perk does is give you somewhere between 1-8(?) bonus herbs after picking up an herb. Below shows you the bonus herbs (+8 and +4 after pick up) I received from picking up elfroot.
I was trying to find out how often the bonus triggers from picking up 18 elfroot herbs in a row. I did around 5 runs.
Here are the results (after farming 18 elfroot herbs):
- Run 1: Gave +12 bonus elfroot herbs.
- Run 2: Gave +12 bonus elfroot herbs.
- Run 3: Gave +10 bonus elfroot herbs.
- Run 4: Gave +1 bonus elfroot herbs.
- Run 5: Gave 0 bonus elfroot herbs.
So yes, even picking up 18 elfroot in a row, you can still get no bonus herbs. As it was stated, its only 10% chance.
Anyway. this is just an idea of the amount of bonus herbs you can get.