Single easiest way to define balance and difficulty in a map is through pickups.
what is a FPS shooter without weapons, ammo, and armor. It's very easy to add these to the maps. You decide where you want it, place the triple marker and the object will appear at that location.
RightClick to add object, and choose PICKUP
Scroll through the available Pickups, which is basically every ammo, weapon, armor and health pickup available. The one thing you may have to concern yourself with is the rotation of the actual model, You may have to adjust the YAW. I'm sure you can figure that out.
One nice touch with alot of the monolith objects is, a pickup like this acts as a junior trigger. At pickup you have the option to send a command, a pickup messahe field is available for a simple or complex message or script.
Pickups influence gameplay?
Just think what might have happened if those ammo boxes were not in the basement lab area of Quarantine, do you think that Survivor type games would play the same way? Ammo pickups draw players to certain areas during MP maps. Place heavy weapons outside common paths to force players into dark areas and dangerous situations.