Clean up option,as the name suggests,is used to Clean up the files by Removing Unwanted points,Empty text paths or objects from the file. It is one of the Illustrator's powerful option,which can save a lot of time &manual work efforts. When we work with a complex shape or artwork.sometimes we face Stray points,Empty text paths,&Unpainted objects.(as shown in below image)

If we deselect these objects they become invisible so it's too difficult for any designer to find &remove objects from the file manually.

We can see these objects in outline mode(Ctrl+y) but in case of complex artwork which is having lots of details in it then Outline mode will not going to work.(as shown in below image)

So Clean UP is the best &easiest way to remove all the unused &unwanted objects from the file. To remove these objects,just go to the Object ->Path ->Clean Up.(as shown in below image)

Clean up dialog box will appear.Then we can select the items that we want to remove from the file &click Ok :-)(as shown in below image)

Here,all the unused elements are removed from the file. &it makes the workflow comparatively faster &technically strong.