Familiars and other animal companions are a staple in fantasy literature, and eagles and falcons have been used to hunt for centuries. How practical is it to use animals in battle?derederest
It depends on the combat role, but animals have seen use in combat.
The big example are, of course, horses. Cavalry would not exist without them. At least, not in our world. Elephants and camels have also been used as cavalry mounts. I’m sure I’m forgetting some others. Many animals have been used in non-combat support roles.
Dogs are another major combat animal. The specialized breeds of war dogs are mostly gone now, but they did see use historically. There is still combat application for dogs today. A dog is far more adept at running down fleeing foes, and they remain a highly mobile skirmishing unit. They also have superior senses of smell and hearing, making them valuable sentries. Even if you don’t have as much control over them than with human soldiers, they’re still quite useful.
None of that’s familiars, though. Animals used in warfare are one thing, but a familiar is a magical “accomplice.”
I’m going to be a bit vague here, because the concept of the familiar isn’t a single thing, it’s varies widely based on the setting. The familiar assists the mage in some way, it’s not generally a combat animal. This is usually something like a cat, rodent, or a small bird. It may not even be an animal, it could be a supernatural creature assuming the form of that animal. Also, depending on the familiar, it’s entirely possible it would be something overtly fantastic, like an imp or small demon.
Depending on the rules associated with a familiar, it may be psychically linked to magic user, meaning mage draws significant advantages from their familiar, such as spying and reconnaissance. In extreme examples, it may even be vital to their ability to channel (or cast) magic. So, these can be very important beings, but it depends on the rules for that setting.
In the real world, there were beliefs that the pets of suspected magic practitioners had intrinsic magical powers, or were proof that someone had entered a pact for their power. The entire idea of the familiar has historical basis, even if the concept itself had no grounding in reality.
You mentioned falconers, and also the use of hunting animals earlier. There is a concept of some varieties of magic users having combat focused animals with them. Again, there’s some history here. A number of animals, including birds of prey and dogs have been used as hunting companions. It’s a distinct concept from the familiar, and also from the use of animals in warfare.
So, there’s several different concepts here, and all three have some historical basis, but they’re all distinct. You probably don’t want to mix them indiscriminately, but there’s also room for blending them together, depending on the rules for your setting.