Archers are not that bad at hand to hand combat at warmaster. So i agree with the others that it can be interesting to let them fight.
Archers are not that easy to use (i think). You have to place them at shooting distance, etc. Not that easy.
To put them in front of your unit garantee you they will fire if the ennemy charges you. As said, if it's you who charge, you can in a simple order tell the rear infantry to advance and contact the ennemy, while your archers just let your infantry pass.
An other solution (to my humble opinion) is to let archers freely circulate in the battleground, in order to seize any occasion to shoot. It generaly means that you keep them on the rear at the beginning of the game, to advance them and shoot after that. But finding non-in-contact ennemy troops is not that easy.
So mainly if you fire at 15mm, it's not that bad to put them on the fornt of your infantry units, to be sacrified to make the ennemy bleed a little.