I don’t think you can do that. LibreOffice is not a collection of programs.
Module for presentations is Impress, for writing text documents is Writer, then there is Calc, Draw and Base (and module for writing mathematical equations).
LibreOffice is just presenting you different feature set depending on a type of document you are editing. And this is not a bad thing. You are not wasting space with all modules installed because they are all, essentially, one program.
You could actually benefit from this.
If you write a text document and all of the sudden someone ask you to make a presentation regarding that document, you could open it and go File → Send → Outline to presentation. Structure of Writer’s document will be imported to Impress (additional corrections may be needed, and only headings will be imported, but you’ve just done an outline in a mouse click).
If you have to send a letter to many people, you could use Calc as a database to hold addresses and names for the mail merge feature.
You could open a PDF file in Draw and save image from that PDF to a hard drive and import it to Writer.
Bottom line: you are only installing LibreOffice and you’re not wasting additional space or resources, at least not in the sense you think you are.