I don't know much about Scavenging, but it's already implemented in the Hungarian server (the latest world has is, started at 28 of november).
But I try to share my knowledge about it.
First of all it has 4 entrances:
- Lackadaisical Looters - 10% of the units plunder capacity
- Humble Haulers - 25% of the units plunder capacity
- Clever Collectors - 50% of the units plunder capacity
- Great Gatherers - 75% of the units plunder capacity
The time your troops spends in one "entrance" depends on the units looting capacity.
Proof:
-
80 spears = capacity of 2000
-
25 LCs = capacity of 2000
If you increase the capacity the troops are going to be away more time.
What I don't know is the exact numbers or the formula. You can test it and figure it out.
The other thing I don't know and could be important is that how to use Scavenging effectively. Obviously you are farming with LC and using Scavenging with the others units (axes or the defensive units, but if you need to send help for someone and you cant because you are Scavenging then it can be a problem, choose your time wisely). By using Scavenging effectively I mean how many troops should be sent into which entrance? Should I send all my troops to the "Great Gatherers"? But then my units are away for half a day or even more. Should I go equally into all the entrances once? And here is I think the formula would be great so you could somehow calculate the numbers how many "capacity" you should send into each entrances to make all the plunders take the same time and even with that. Does it more effective? So this is the point where I can't help you.
Closing thoughts about when you should use it, but it's still a new feature so improvement can be made!
Actually you can use it on the first days of the server instead of farming (with the spears and swords from the quests). Because you can unlock 2 entrances easily even 3 in the first 2 days. And on the .net servers the barbarian villages ratio to the player villages is so low (in Hungary it is really high) so a lot of players farming the same barbarians and instead of looting 1-1-1 for a 1-2-3 hours run, you can plunder 100 or more under 30-40-50 minutes in entrance 2 with the basic spears-swords. (
picture)
Not a world reached mid-game or late-game with Scavenging yet (as far as I know). But if you know about a day where you are going to farming only then you can send to Scavenging your axes. If you are in the midle of the "blue-sea" you can Scavenging with your defending troops as well. So I think this feature gonna speed up the mid and lategame as well.
(AND FINALLY defensive players got something I mean an off player can still make more out of Scavenging and farming but I felt like over the years defensive players got nerfed and attackers got buffed over and over -this last bracket is only about my feelings, sorry-) .
Who benefits more? Not sure. I think it helps the less experience and inactive players and even active/good player can make a lot from it. On the Hungarian server with 2 villages
I make my daily plundered resources' 10% by Scavenging.
I'm sorry for my grammar and spelling mistakes. English is not my native language and I wrote this only for helping those who wants some info about Scavenging. I could miss out important things and someone can easily know more about this than me. This is only the information that I know about Scavenging. I hope this knowledge will be useful for someone. ^_^
Mary Jane the 420Th 
