Impolite attacks
You might be thinking:
'Why can an attack be impolite? I help other players in defeating their legions - so I don't understand, why this can be impolite?!?'
Two reasons:
1.
Let's imagine that your attack strength is 250.
Now if you fight a legion with 251 remaining health, it leaves exactly 1 remaining health point! However, this legion splinter must still be attacked with many villagers in order to have a 100% chance of victory (see also: Probability of Victory). This is absolutely inefficient and means a huge waste of attack resources!
Remember that the main reason for attacking legions is for the resistance points (RP) earned. The number of RPs earned depends on the health removed from the legion by the attack. Removing health points gives RP equal to the health points plus a factor of 1 to 1.35 (max. 20% resistance bonus + max. 15% guild bonus). Example: 200 health points gives a maximum of 270 RP - as long as there is no bonus weekend. So removing the last 1 health point gives 1 RP for this attack.
But the loss of strength and resources (durability of weapons, shields and helmets) is just as high as against a legion with maximum health.
It doesn't break any rules, but it's unfair to the village owner or guild members who have to waste their resources on it!
As such, it is impolite to attack legions and leave them with low health. There is no official "limit" on how much health should remain. The strength of the legion plus 19 would be a value that can serve as a very good guide.
2.
In some cases some players want a legion not being defeated and reach their village. (eg. when achieved resistance level 10 and want to gather the rewards for reaching the resistance levels again). Since there is still no 'flag' implemented where a village can tell other players NOT to hit legions of this village there is a common practice (just working with resistance level 10):
If you see a legion with full health (2,300) that legion should NOT be attacked.
The first attack on the village legion must be carried out by the village itself. Then the legion's health less than 2,300 and with that all players know that this legion can be attacked.
Some guilds / players seem to have a rule also for smaller legions that only the village owner should hit an 'untouched' legion, i.e. a legion whose current health is 2300, 1900, 1800, etc.
Planning your attacks
If you are planning to completely finish off a legion's health by hitting it yourself, and are not expecting others to hit it, then you could avoid your final hit being inefficient by 'pacing' your attacks. You don't need to think about this when starting off hitting a legion that has a lot of health such as 1,600+.
When the legion gets to lower health e.g. 800 and your maximum possible attack strength is e.g. 250, then you could hit it three times, removing 250 health each time, but then the legion would be left with 50 health. It would be more efficient, in terms of RPs gained for resources used, to attack the legion four times with a strength of approximately 200.
Of course there is always the possibility that some other player will attack the legion and unintentionally spoil your plan.
There is a way to finish off a legion with low health (equal or less than 50) without wasting villager resources.
That is to attack it with just Asterix or Obelix.