Doubts about multiresolution!

Hello everyone!
About Multi-resolution. I would like to know if my rationale for functions such as Delete Higher, Reshape and Apply Base is right.In Delete Higher I understand that it is when having x subdivisions and returning an earlier one and applying to delete what was done in the front I lose.In Reshape the concept I understood is that I have a mesh and duplicate and with that I can copy the details from one to another.In the Apply Base what I understood a apply changes and when applying later going to the edit mode I have as base mesh.What is right or not what I said.Could you tell me if there was something missing in my doubts and what sense these functions have in digital sculpture.Thank you!