Doubts about multiresolution!

Doubts about multiresolution! The multiresolution functions like Delete Higher, Reshape and Apply Base.What I understand is that the Delete Higher when returning to a level below and clicking on the option I lose the level above.Reshape your I have a mesh and by duplicating it when selecting one and then the other I can copy from one to another the details having them equal levels.In Apply Base I change the shape of my mesh base in sculpt and when applying the function my mesh will be modified to a new mesh base.What could help me about this!I'm conceptualizing right!What these functions have to be useful in sculpture!
Thank you!