I believe we should always ask forgiveness because we need forgiveness. None of us are perfect. Therefore we require forgiveness. And for those that prefer to maintain a rather shallow POV what have you got to lose, the forgiveness is free after all.
God's blessings can be blocked by unforgiveness, IMHO, by the fact He is a righteous and just Lord, by us maintaining a state of unforgiveness that prevents us from moving toward a righteous state of being. We choose to be unforgiving, we therein choose to be unrighteous, this is uncompatible with God's nature.
God bless you