Using Mercenaries

[Roark]

As the Byzantines, I use mercs a great deal for my invasion forces. The Byz just can't field good spearmen or polearms otherwise.

Playing as Catholic factions, I usually shop around for the best available horse archers and siege equipment (Merc Mangonels). For some reason, I'm always a little bit behind in my development of artillery.

[Martok]

Playing as Catholic factions, I usually shop around for the best available horse archers and siege equipment (Merc Mangonels). For some reason, I'm always a little bit behind in my development of artillery.

I also hire out artillery crews--particularly mangonels and trebuchets, since of course it takes a while before can train them myself. Aside from that, however, I don't use mercenaries very much. I'll hire out the occasional heavy infantry/cavalry unit, depending on my needs, but that's pretty much it. It's not that I don't like mercs; but they're generally too expensive to be worth it. I'll hire them as needed, but for no longer than is necessary. I always replace mercenaries in my employ with my "home-grown" versions as soon as I'm able.

[Cowhead418]

I use them when I'm getting ready for a large invasion of a province where the enemy has lots of troops. I usually have a few provinces with inns and I wait for a turn with plenty of mercenaries for hire. On that turn I hire as much as I can afford and attack. The mercs take the brunt of the enemy fire and therefore will take most of the casualties so I can keep my "home-bred" troops safe. They will also stay to take some of the casualties in sieges. After I conquer the province fully I usually disband unless the mercenarie unit(s) can still be useful.

[el_slapper]

As others. Plus this detail : they cost much to stay alive. So they are used as cannon fodder, while regulars must get most of the kills.

[matteus the inbred]

they cost much to stay alive. So they are used as cannon fodder, while regulars must get most of the kills.

couldn't agree more. they're there to get killed, not paid!

except merc artillery, as Martok and Roark said. very handy to whip up a couple of mangonels for that tricky siege.

my favourites are Rus and Italian spears instead of the rubbish ones you get early on. and Arab swordsmen, although it's amazing any would want to be hired by me, their survival chances are...low

[Loucipher]

Couldn't agree more with what was said.
For me, mercenaries are good for:
1. Quickly mounting a diversion attack somewhere, so that enemy uses up his resources before I commit my national armed forces.
2. Leading the suicidal and sacrificial attacks during battles or assaults (a unit of mercenary men-at-arms getting shot to pieces or ridden down by enemy knights saddens me far less than a unit of my own troops in such situation).
3. Keeping an eye on besieged castles (and suffering losses in such cases) while my own troops are out winning field battles.
4. Training my spies on low-loyalty generals and my assassins on low-command generals (most of mercenary units aren't really good at either).
5. Supplementing my own armies with units I can't train normally, but would like to have for some mysterious reason (e.g. Armenian Heavies, Khwarazmians, various siege equipment crews, Vikings (in early) an so on).
All uses except 5. lead to one corollary, ingeniously pointed out by Matt:

they're there to get killed, not paid!

Excellent words! To that extent, I use mercenaries only when at least one of these conditions are met, and have no second thoughts about sending them into potentially catastrophic positions. For example: as far as I'd never order a unit of my own missile troops to charge into the fray after their missiles are spent, I'd give such an order to mercenaries without even batting an eyelid, just to provide more bodies to throw at an enemy. On the other hand, I try not to put them in positions where their rout might affect morale of my national troops - after all, they still wear my colours, at least for a while...

[matteus the inbred]

as the saying goes, soldiers are there to make a living, generals are there to make a killing...

even the very best merc regiment will take enough casualties to make it not worth fielding sooner or later (sooner... ), and you can't replace the casualties, so never get attached to them.

inns are something i now build almost everywhere, as they improve loyalty as well. for factions with crappy starting troops or big gaps in what they can field (Byz, HRE, French) and a serious need to kick butt from the start, mercs are the answer.
good in VI too, you can hire nasty Viking stuff and crossbows!