You should stop gathering resources if the resources have 2/3rd left or less. Here is a helpful table to remember when to stop:

• 1/1 - always free to gather

• 1/2

• 2/3 or 1/3 - both will regenerate one per day but leaving it at 2/3 is safer

• 8 / 13

• 10 / 16

• 13/19

• 14/20

• 20/30

• 21 / 32

• 26/40

• 66/100

• 200/300

Added some more details :)

My preferred 'safe limit' for a source: X/1.5, round down, where X is the capacity it can hold. Enough quantity to replenish ~full capacity.

For examples, 8/8, 8/1.5 = 5 safe limit, could replenish to 7.5 ~8. 10/10, 10/1.5 = 6 safe limit, could replenish to 9. 20/20, 10/1.5 = 13 safe limit, could replenish to 19.5 ~20.

If I see below my preferred 'safe limit', of course, I leave it as is. Sharing is caring, we already have low population. Someone tagged me as a muppet. Yep, I rather be a muppet than like that greedy-@$$ mf.