About inclusion of buildlink in a buildlink

[Mayuresh <mayuresh%acm.org@localhost>]

Trying to create buildlink of wip/sylvan package. Trying to understand the
following comment:

# XXX Uncomment and keep only the buildlink3 lines below which are # directly
# XXX needed for dependencies to compile, link, and run.  If this package
# XXX provides a wrappered API or otherwise does not expose the APIs of # the
# XXX buildlink3 lines below to dependencies, remove them.
#.include "../../devel/gmp/buildlink3.mk" 

Say, the package wip/ltsmin is going to include buildlink of sylvan.

Now sylvan's Makefile already includes buildlink of gmp.

If ltsmin uses gmp directly, it would directly include its buildlink.

So what exactly is the role of including buildlink inside buildlink?

-- 
Mayuresh