Whenever you have way more weight/traction on one side causing the other side to lose traction, like this:
0 - 24 seconds = diff unlocked
25 - end = locked
As you can see, the back left tire had an exceptional amount of traction. However, due to the diff being unlocked, the back right and front left tires just spun. Once the diff was locked, it forced the back left tire to turn resulting in getting up the bump. This is not the way you would approach a little bump like this as I did this for demonstration purposes only.