Throwing spears can be useful if you've got the spare points… think of it like this, if it kills one or two enemies in a game, then they're paid for.
They lend themselves to the idea that rohan is a skirmish based army that harasses, weakens the enemy, charge where they're weak and run where they're strong kind of play and I've done this (and heard of others) doing this effectively in the past.
I don't base my strategy on them any more. the moving penalty with throwing weapons makes it tough, but let's do the maths.
You move to harass the enemy with 12 troops with throwing spears.
On a five plus, 4 of those shots should hit.
Against D6 or D7, you've got a 0.6 chance of killing. So every two turns you statistically you should kill just over 1 if 4 hit. In 10 turns you should kill 6.
Against D4 or D5, this increases to 1 in 3 chance, so 1.33 should die each turn if 4 hit on average. In 10 turns you should kill 13.
Against D3, this increases to 50:50 so in theory, if the statistical 4 out of 12 hit for each move and throw, 20 should die over 10 turns of 12 throwing (2 per turn)…
Of course, it won't always work out like the above, but you can cost it up. 12 Throwing spears is 24 points. So you'd need to be killing 4 orcs with spear, shield or bow, 2 warg riders, 2 black guard of barad dur, or three of most other things.
So can they pay for themselves? Yes. Will they pay for themselves? Not always! It's a game of chance as well as strategy after all
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