For example, you could pour all your starting Ability points into Two-Handed Weapons, but then only run around with a dagger and a shield. However, the possibilities also mean you can theoretically break your game before it begins. Naturally you can go with the basic route of a melee fighter backed up with a healer, or a wizard who does massive damage backed by a sneaky rogue who backstabs everyone. It is in your best interest to create your first two characters in such a way that they complement each other. All that matters is whether you're applying points to the areas that work for your playstyle.
However, if you are customizing, the class you choose is actually meaningless. Abilities, Talents, and Skills all have prerequisites, thus introducing the balance. If you're a veteran of role-playing games or desire control, you can customize every aspect of your characters. Your characters can be assigned a class from a list of eleven Preset Classes, but these classes are merely presets to the myriad of skills, talents, and spells you can assign. When you first start a new game, you are tasked to create your first two characters, both in appearance and starting skills. Character creation in D:OS can be a fairly long and involved process if you choose.