In other words, they wander around thinking deep thoughts about the meaning of life and why Omni-Tek decided to give them only three tentacles instead of four. Then along comes Joe Adventurer who decides to use those tentacles for target practice. Combat has started. If the mutant has a ranged weapon, it'll get into firing range and start to return fire. If not, he'll be in your face for that up close and personal feeling.
Insurance is a wonderful thing.
There's more to it than clicking the attack key. Each weapon has skills associated with it such as Shotgun or 1-Hand Edged. Some may even require multiple weapon skills to use properly. So naturally you want to keep both skills as high as possible if you plan to use that weapon. Weapons may also have additional attack types available.