I'm recently starting to make use of the Summon Familiar/Imp spells. FOr those not aware, they cost a permanant 1HP from your soverign to summon, and they're fragile little creatures who can cast every spell (but not skillls) that the sovereign can, albeit without the soverign's spell mastery or spell damage bonuses.
They're immensely useful for things like hasting yourself or throwing various debuffs onto enemies, or casting heal. They're fairly useless at offensive spells due to no spelldamage bonus, or manacost reduction, but anyway that's besides the point.
By default, a familiar starts with a mere 10 HP, and 0 defense. They get some extra hp per level, but it's not much. I could swear it's less than 2 HP per level.
these creatures are technically melee attackers. they have a weak and rather pointless melee attack that they can use if you're desperate. But the problem with that is that they get placed on the frontline besides other melee troops.
By contrast, you may notice that whenever you have archers in your army, they usually get deployed in a secondary line behind your melee units, starting them farther away from the enemy, and most likely safe behind your melee's zones of control. I think familiars should be treated like archers and automatically deployed in that rear line too.
Currently, because of their low hp and defense, they are the number 1 target for the AI. They're weak enough to wipe out in one hit, many times, and their initiative is average at best so you can't count on gettting a turn to move away before the enemy gets you. The biggest threats are fast moving things. wolves, horseback units, skaths, etc. Nature is full of things that, for some reason, have five base movement, and are happy to beeline for the easiest juicy target and nom it in one gulp. It gets to the point where having a familiar is just frustrating and it's more trouble than they're worth to keep them alive.
You just have no tools for enhancing them, they're not champions and so can't be given most of the buffs you'd normally use on a champion (stoneskin and courage!!), they can't be given equipment or traits either. But having a second spellcaster with such flexibility IS an amazing thing.
In my current game, i had to focus on building up initiative with the rest of my army, and i move two units into a defensive position to cover the familiar at the start of each battle. some things are still faster though ;-;