Different tactics for the English

[caravel]

The general of that army made sure to send a message to the Spanish by not ransoming any of them back. It broke the Spanish. The Almos saved me the trouble of risking Excomm by picking up the pieces themselves.

I never execute prisoners on the field. The only thing you can gain from this is dread, and I never see my generals needing or lacking, this attribute. Dread is of no use on the battlefield it affects provincial loyalty and only applies to the faction leader and governors. The most important things to consider are that if you capture, e.g, 1000 men there are 2 possible scenarios:

1) The AI accepts the ransome and pays, this means:

a) You get paid, alot if nobiles or royalty are among those ransomed, you deprive him of funds.
b) He gets alot of battered demoralised troops to support and use again, with lower loyalty. He may have difficulty training new troops as he's just paid a big ransom and has to support this demoralised rabble and their general.
c) He gets back the, possibly, "good runner", and diminished loyalty general. As it used to say in Shogun "let this continue".
d) The rest of his forces aren't going to be happy with the defeat, add the low loyalty ransomed back force to this and you could have the recipe for a good old guerra civil.

2) If the The AI refuses to pay, he loses those men who may well not have gained any vices, and whose loyalty may not have been hit too badly, and it affects loyalty among his generals and could trigger a civil war.

If you had executed on the field the general would gain one of the "butcher" type vices ("scant mercy" etc) which are not all good as some of them affect morale.