The animation will be started immediately using SnapshotAndReplace. Call Start(AnimationTransition) if another type of transition (for example, a fade-in) should be used.

Important: When animations are started or stopped the animations do not take effect immediately. That means the new animation values are not immediately applied to the properties that are being animated. The animations are evaluated when the animation system is updated (see Update(TimeSpan)) and new animation values are written when ApplyAnimations is called.

The method UpdateAndApply can be called to immediately evaluate and apply the animation. But in most cases it is not necessary to call this method explicitly.

Reference