It's all part of the strategy. Skills aren't manitory until you run into the situation that you will naturally, and are most effective to use them. Impale is used if you want to attack and dispatch an enemy ahead of you without having to do additional moves. As with Jump attack is more of attack/evade or attack/aggression tactic where you need to get away at tight situations or blow through your victom in a haste.
Think chess.
To further explain, open Berzerk! and pick Massacre, and then set Strenght 14, Endurance 12, and Dex 12. Distribute the rest to whatever suits your play style, or all on willpower to effectively use the skills later. Now put a point on Running, Impale, and JumpAttack...
While playing, think of your goals, and what you've put on your trusty strategy guide. You want all your enemies in one direction so you don't get surrounded, or get away from a later threat when oppose by a bulldemon or multiple powerhouses. This is where Impale, and JumpAttack comes to play. Know that these skill consume a ton of E so plan wisely ahead of your uses. When surrounded or two bulldemons are coming in your direction, use a jumpattack on the closer enemies that have a space behind it. It's a great "getaway" tactic and luckily will dispatch your enemy in the process. Impale is great for aggression when you score a knockback on one of your meat demon, or are at charging distance.
Play with this idea, and soon, you'll have even more strategy to add to your guide. =1