Optimizing a Makefile
I think the suggestion in the link you mention is to not bother with making your object files "intermediate".  I tend to agree.

If make deletes the object files after the link step then it has to re-build them all at the next invocation of make.  Without this, the next time you make, it can look at the dependencies of the object files (as specified by the makefile, the part after the :) and only rebuild them if the stated dependencies have a later timestamp.

You might also want a make clean target to remove the objects via rm, so that you can delete them when you really want to.  But the typical workflow for using make is to keep your object files around for extended periods and type make when you want to build what you've changed.